Hey QQ,
I'm with CharlieC on this one! No sure about UPZ's... but switching out "tongues" on Track 700's is not "plug and play" and I would not want to be spending time going back and forth during the season.
So, even "simpler" in my opinion............ have another (softer) boot altogether just for your pow setup. My pow specific ride is a Moss PQ60 with Track 325's with TD3 SW SI's with 3/3 cant disks at 55/50 angles (yes I'm a mutant and yes I've tried reducing angles on wide boards to no avail) ......and it will carve and I ride deep open pow or deep tree pow no problem.
You speak a lot about your "boot situation".... but no mention of the board your trying to make work with plates and hardboots for pow ??
You could use one setup for everything but some facet of your riding and the board will suffer. It was fun and less to deal with riding the Moss everyday in all conditions but I was beating the crap out of my last Moss using it everyday/everywhere....... and as fun as the Moss is/was to carve and use in the pow there is no substitute for a big carving stick for hard charging carving!
So I got more specific: Pow = Moss PQ60 and a softer flex hardboot and lower cants
Everyday work conditions, groomer carving to chop and slush = Swoard Dual II 168 Track 700's, TD3 SW SI's 3/6 cants
Big GS turns in open terrain carving = Coiler EC SS 177 Track 700's, etc........
Hard charging (turny) carving in tighter and or congested areas = Kessler 168, Track 700's, etc.......
It might sound complicated but it has actually streamlined my riding selection..............it's either a pow day (setup) or not and either way it's always a "one set of boots' day! On non pow days I'll usually have a couple of boards along in the car or on the hill and start out on the big GS board when it's less crowded and switch to either the turny Kessler or the All Mtn. Swoard as conditions/crowds and my legs dictate.
Hope this helps.................. don't give up on hardboots in the POW!