I have an upcoming trip all with AA flight numbers, but two legs are on BA metal. I can now select/change my seats on the BA legs from the AA web site with a temporary automated redirect to the BA website. I noticed that on the BA legs, the AA web site had the "Change Seats" link activated. When you click on it, you are taken to the BA website and can choose your seats. When you are done it returns you to your reservation on aa.com. Very nice integration!!!