Originally Posted by
jsloan
if you're trying to up-fare a single segment out of a longer itinerary, you're likely to run into an extremely high fare difference.
Yeah, even if UA were to do a courtesy change fee waiver, this is not a practical strategy because the entire ticket will refare. You'll either have to buy up to the new fare on the entire itinerary, or you'll create a broken fare (which probably violates fare rules and is thus not possible on a TATL).