Originally Posted by
thephirm
You could also try waiting until you're at the airport and only then ask an agent to change the FF number. On my last flight someone in the SFO lounge had the agent there change the FF account for his ticket from BA to AA without any apparent issues.
That is certainly good advice as a fallback position, but it's also the most likely to go wrong, depending as it does on a clean interface of data back to the relevant frequent flyer card administration. There are certainly plenty of cases where this goes wrong, even when the boarding pass is reprinted with the correct information on it. On the other hand that boarding pass is very valuable evidence in the event of a dispute!