Originally Posted by
SuperFlyBoy
Well, the one time I tried, the younger GA at HAM (who just arrived at the gate, luckily!) was able to do it for me, but 2 older types that I first me flatly said that they couldn't.... (this was about 2 years ago, btw)
It worked sometimes at the check-in at MUC, when I flew MUC-FRA-XXX and the upgrade cleared in MUC in advance for my FRA-XXX flight.