This topic has certainly wandered!
I am not going to argue the deep-down secrets of Windows with you - I am at best an 'intermediate level tinkerer' and likely to get myself in trouble with some of my tinkering. BTW using Win XP, SP2.
But ... your categorical statement that it 'does not do roll-backs' is seemingly false based on first-hand experience!! I'm certainly getting the symptoms I would expect for a roll-back.
I will assure you that the Restore function does indeed permit me to switch back and forth between versions of QW as I stated earlier. I verified this occurred by opening the 'About' window and I see R! has changed to R2 and vice-versa. It was further confirmed as the behavior problems of the alternate versions was repeatable as I switched. At least one other poster has indicated, as an aside, that it worked for him.
This may not have been the intent of Restore. It may not be recommended. But it works for me.