Pretty funny stuff...Makes me want to check the plates on my squad car even. BRB... ok, I'm safe.
Seriously, it' probably would have been safer to just put the plates over the top of your buddies existing plates. But no harm no foul. Had be heen stopped, he would have been responsible for the plates. Some officers probably wouldn't see the humor in all of that either. I personally think you one-upped him pretty good. Nice work.
Of course, given the whole gay cop thing, I'm def rooting for your buddy to get you back even worse. It's a matter of principle- nothing personal.