// Initial

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
            [2] => Array
                   (
                   [0] => 3
                   [1] => 4
                    )
        )

)

// Final

Array
(
    [0] => 'text'
    [1] => 1
    [2] => 2
    [3] => 'bla
    [4] => 3
    [5] => 4

)