[super vw]

Yeah, thats possible.... kinda like a bezzel or whatnot. if thats the look you want. to me that would stand out to much and look kinda weird. unless it blended in by painting them body color.

You dont need a machine to punch them, you use dies i think that are moble, they kind of act like a hammer and a dolly, the dies would have a positive and a negative side (if you get that) the positive on one side of the metal and the negative on the other (usually the back side) and when they are squashed together on each other they would form the indent/step or whatever. you might be able to make your own dies on a lathe if you have access, you then could make any sort of shape you want.

But i like your idea of covering up a hole like you said, easier perhaps.
Depends on how you want it to look.

Then onyl resson i can think of to even have the vents is to let exhaust heat excape from the rear easier... who knows even if anything will benifit from it?

Later,
Jonathan