It does return the parameter given. If what was desired were simply to filter out elements and return selections, some grep procedure would be perfect for this, as you show in your examples.

What I am wanting to do is something that's probably wrong to even try and do.

I want to grab @_, iterate with shift- some elements will be discarded, elements not discarded will be changed into something completely different- and returned.

I was fantasizing of even using the @_ list to return as well.