I'm GLD and paid $81.93 x2 for MCE seat 17L but after reading some seatguru reviews I decided that 19H will be nicer. I called and requested the change for my inbound and outbound flts b/t DFW and LHR. After a long (30 min total) wait they said they had changed but it required some manual work. Later I checked and only one had been changed so I called back. This time I waited about 10 min before hearing that I'd have to pay an additional $82 to make the seat change. I asked if I couldn't apply the $81.93 that I'd already paid and they said it doesn't work that way and that I should stay in 18L. I suppose I'll HUCA.

Online if I make the seat change it appears to go through but when I reload the reservation the seat doesn't change.

I see the rule about not getting a refund if you switch to a cheaper seat but I'm surprised I can't pay extra (7 cents in this case) to choose a better one.