Originally Posted by
sbgmiles
I have had luck doing this for my husband. I wait until right before he wants to check-in. I call the general Aadvantage number and when the automated system asks for his AA number, I say that I don't have one. I then get routed to a general number where they do not seem to know the rules. I ask to have them change his AA number to his BA number. I have done it about 4 times in the past year and his seat assignment remained, but he did lose priority boarding.
Your husband might have a positive experience in the past but once things go wrong, there is no way back on AA flights.
It's definitely a YMMV situation and it's the risk of the passenger to take it.