Well, map() is a good alternate solution (though it wouldn't be doing the modification in place exactly.) But, you didn't show how to use it in the way he wants to...

@list = map { $_ eq 'condition' ? my_sub( $_ ) : $_ } @list;
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and yes, that'll work when my_sub() returns a list too.

-sauoq
"My two cents aren't worth a dime.";