Have a int'l flight booked with UA and excursionist perk. Wanting to change return leg to IAD, which is currently booked @ YN fare for discount economy @40k mi. If the redemption cost for that fare increases, would that be applicable when considering change options? I'm assuming if I want to avoid paying more miles, I need to find another flight available for same 40k mi?

I ideally wanted to return to smaller airport, but UA redemption rates changed in the 7 days!!!! it took to xfer CUR to UA miles. Thus, I stuck with IAD return for availability hoping rates might drop in the coming 6+ months knowing worst case i can get ground transport from there. Didn't want to shell out 10-20k per person extra miles for multiple individuals traveling for something where availability is regularly changing (an excursionist flight of *A partner seems to be disappearing/reappearing even though flight is over 6 months away).

Thanks!