Jak wstawić nową parę wartości klucza w tablicy w php?

Mam tablicę o następującej nazwie$test_package_data. Dla odniesienia drukuję dwa pierwsze elementy:

Array
(
    [0] => Array
        (
            [test_pack_id] => 9f27643023a83addd5eed41c4aade840
            [test_pack_name] => Exams Combo
            [test_pack_desc] => This Package contains 24 tests of Reasoning, English and Quantitative Aptitude.

Total Tests in this Package : 26
            [test_pack_type_id] => 3
            [test_pack_image] => 
            [test_pack_validity_year] => 0
            [test_pack_validity_month] => 3
            [test_pack_validity_days] => 0
            [test_pack_plan] => paid
            [test_pack_price] => 399.00
            [test_pack_no_tests] => 0
            [test_pack_publish] => yes
            [test_pack_sold] => 1
            [test_pack_created_staff_id] => ff8d4a5ea6bf11dce105aa2fa7b959b8
            [test_pack_updated_staff_id] => 81c4e3607c7e56bbf5461ef150437675
            [test_pack_created_date] => 303
            [test_pack_updated_date] => 1349235701
            [test_pack_purchase_date] => 255
            [category_detail] => Array
                (
                    [0] => Array
                        (
                            [test_pack_category_id] => 8
                            [category_name] => English Language
                            [test_detail] => Array
                                (
                                    [0] => Array
                                        (
                                            [test_id] => 91
                                            [test_name] => English Language 8
                                        )

                                    [1] => Array
                                        (
                                            [test_id] => 90
                                            [test_name] => English Language 7
                                        )

                                    [2] => Array
                                        (
                                            [test_id] => 88
                                            [test_name] => English Language 6
                                        )

                                    [3] => Array
                                        (
                                            [test_id] => 89
                                            [test_name] => English Language 5
                                        )

                                    [4] => Array
                                        (
                                            [test_id] => 87
                                            [test_name] => English Language 4
                                        )

                                    [5] => Array
                                        (
                                            [test_id] => 86
                                            [test_name] => English Language 3
                                        )

                                    [6] => Array
                                        (
                                            [test_id] => 85
                                            [test_name] => English Language 2
                                        )

                                    [7] => Array
                                        (
                                            [test_id] => 97
                                            [test_name] => English Language 1
                                        )

                                )

                        )

                    [1] => Array
                        (
                            [test_pack_category_id] => 4
                            [category_name] => All Subjects
                            [test_detail] => Array
                                (
                                    [0] => Array
                                        (
                                            [test_id] => 93
                                            [test_name] => Mega 2
                                        )

                                    [1] => Array
                                        (
                                            [test_id] => 92
                                            [test_name] => Mega 1
                                        )

                                )

                        )

                    [2] => Array
                        (
                            [test_pack_category_id] => 7
                            [category_name] => Quantitative Aptitude
                            [test_detail] => Array
                                (
                                    [0] => Array
                                        (
                                            [test_id] => 83
                                            [test_name] => Quantitative Aptitude 8
                                        )

                                    [1] => Array
                                        (
                                            [test_id] => 82
                                            [test_name] => Quantitative Aptitude 7
                                        )

                                    [2] => Array
                                        (
                                            [test_id] => 81
                                            [test_name] => Quantitative Aptitude 6
                                        )

                                    [3] => Array
                                        (
                                            [test_id] => 80
                                            [test_name] => Quantitative Aptitude 5
                                        )

                                    [4] => Array
                                        (
                                            [test_id] => 79
                                            [test_name] => Quantitative Aptitude 4
                                        )

                                    [5] => Array
                                        (
                                            [test_id] => 78
                                            [test_name] => Quantitative Aptitude 3
                                        )

                                    [6] => Array
                                        (
                                            [test_id] => 77
                                            [test_name] => Quantitative Aptitude 2
                                        )

                                    [7] => Array
                                        (
                                            [test_id] => 76
                                            [test_name] => Quantitative Aptitude 1
                                        )

                                )

                        )

                    [3] => Array
                        (
                            [test_pack_category_id] => 6
                            [category_name] => Logical Reasoning
                            [test_detail] => Array
                                (
                                    [0] => Array
                                        (
                                            [test_id] => 75
                                            [test_name] => Reasoning 8
                                        )

                                    [1] => Array
                                        (
                                            [test_id] => 74
                                            [test_name] => Reasoning 7
                                        )

                                    [2] => Array
                                        (
                                            [test_id] => 73
                                            [test_name] => Reasoning 6
                                        )

                                    [3] => Array
                                        (
                                            [test_id] => 72
                                            [test_name] => Reasoning 5
                                        )

                                    [4] => Array
                                        (
                                            [test_id] => 71
                                            [test_name] => Reasoning 4
                                        )

                                    [5] => Array
                                        (
                                            [test_id] => 70
                                            [test_name] => Reasoning 3
                                        )

                                    [6] => Array
                                        (
                                            [test_id] => 69
                                            [test_name] => Reasoning 2
                                        )

                                    [7] => Array
                                        (
                                            [test_id] => 68
                                            [test_name] => Reasoning 1
                                        )

                                )

                        )

                )

        )

    [1] => Array
        (
            [test_pack_id] => e7e95de96987cc7c89c1f0183110fb38
            [test_pack_name] => Aptitude Reasoning
            [test_pack_desc] => This package contains 8 tests on Reasoning.
            [test_pack_type_id] => 3
            [test_pack_image] => 
            [test_pack_validity_year] => 0
            [test_pack_validity_month] => 3
            [test_pack_validity_days] => 0
            [test_pack_plan] => free
            [test_pack_price] => 0.00
            [test_pack_no_tests] => 0
            [test_pack_publish] => yes
            [test_pack_sold] => 4
            [test_pack_created_staff_id] => ff8d4a5ea6bf11dce105aa2fa7b959b8
            [test_pack_updated_staff_id] => ff8d4a5ea6bf11dce105aa2fa7b959b8
            [test_pack_created_date] => 303
            [test_pack_updated_date] => 1347127387
            [test_pack_purchase_date] => 110
            [category_detail] => Array
                (
                    [0] => Array
                        (
                            [test_pack_category_id] => 6
                            [category_name] => Logical Reasoning
                            [test_detail] => Array
                                (
                                    [0] => Array
                                        (
                                            [test_id] => 75
                                            [test_name] => Reasoning 8
                                        )

                                    [1] => Array
                                        (
                                            [test_id] => 74
                                            [test_name] => Reasoning 7
                                        )

                                    [2] => Array
                                        (
                                            [test_id] => 73
                                            [test_name] => Reasoning 6
                                        )

                                    [3] => Array
                                        (
                                            [test_id] => 72
                                            [test_name] => Reasoning 5
                                        )

                                    [4] => Array
                                        (
                                            [test_id] => 71
                                            [test_name] => Reasoning 4
                                        )

                                    [5] => Array
                                        (
                                            [test_id] => 70
                                            [test_name] => Reasoning 3
                                        )

                                    [6] => Array
                                        (
                                            [test_id] => 69
                                            [test_name] => Reasoning 2
                                        )

                                    [7] => Array
                                        (
                                            [test_id] => 68
                                            [test_name] => Reasoning 1
                                        )

                                )

                        )

                )

        )
)

Teraz chcę dodać nową parę klucz-wartość o nazwie[count] => '$some_value' w tej tablicy w każdym elemencie po parze klucz-wartość[test_pack_purchase_date](powiedz po[test_pack_purchase_date] => 255. Jak mam to zrobić? Czy ktoś może mi w tym pomóc? Z góry dziękuję.

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