Originally Posted by
eeflyer
Another option is if I am able to take the credit for the return leg and apply its residual value on a different leg? Is that possible?
The residual value will likely be negative. When you change the itinerary, UA will reprice it to match your actual flights -- so you're back to $4200 unless your 'different leg' happens to be a return trip to TYO, in which case you wouldn't have this problem in the first place. :-)