TL;DR: I have a few questions to figure out what's easier. Sorry if some of these have been asked before, but my searches yielded nothing.
1) Can I taked back an RPU for a confirmed upgrade and take my place in the CPU queue? When is my 'deadline' for this to go smoothly?
2) When is the last time I can apply an RPU for a confirmed seat if R>0?
3) If R=0 when is the last time to jump ahead of the CPU list?

Long version:
I have a redeye SMF-IAH in early May. As usual there's a few in F and E+ is almost empty (E- is filling up, so hopefully this won't be down-gauged), so at a month out it's holding at elite-light. While IAH redeyes usually stay elite light the Thursday departure and airbus F/Y ratio have me a little worried about my CPU chances. Lately I've just been watching the seatmap/R-count, but now my xIAH connection is filling up. I'm not 'worried' about upgrading on this flight, but if I'm going to use an RPU I'd rather it clear on both flights.

If I apply an RPU for confirmed upgrade (R7) now could I take it back the week before (I can usually tell if things are looking good for me by then)? As I mentioned I'd slightly prefer this since if I'm going to use it I'll also get my connection upgraded.

If that too messy to deal with, what are my options for throwing the RPU down at the last minute if my odds aren't looking good?