对数组的一部分执行某些操作，然后将其重新插入到数组中？

I am creating an array as such, splitting a string by every -:

$array = explode('-', $mystring);

I know I can then implode the array back into one string, eg:

$mystring = implode('-', $array);

But I first need to do something with the 3rd array element and reinsert it into the array before re-concatenating it. Here I am a bit stuck - I cant find any good resources showing this online.

Can anyone point me in the right direction?

you can simply access the third element and reinsert it into the array before imploding

$string = "Foo-Bar-Foo2-Bar2";
$array = explode("-", $string);

$third = "Something else";

$array[2] = $third;
$string = implode("-", $array);

print($string);

Results

Foo-Bar-Something else-Bar2

or you can even directly edit the entry

$array[2] = "Something else"