I have a similar question although I haven't commenced travel. I have an int'l itinerary on a W fare for Sept travel. I'd like to change the return flights. I know I'll incur a $250/pp change fee for making the change. When I price out the new itinerary, it shows that the total fare is about $200 less.

When I looked at making the change online, UA.com doesn't reflect any fare difference in my favor -- it just states $0 and then $250 for change fee. Before I call, I thought I'd ask here if I'm entitled to the fare difference and whether I can credit that towards the $250 fee, or whether I have to pay the $250 fee and then get a paper voucher or $$ in my Travel Bank for the difference.

Also, if I'm confirmed in C using GPUs on the outbound, am I risking losing those by making the change on the return? I'm worried that they'll have to re-ticket the entire itinerary and I'll lose the upgrade in the process.