Welcome down from Lurkerspace!
Be sure to read the thread about the elite status challenge AA offers - it gives you a very decent short cut to AA status.
http://www.flyertalk.com/forum/ameri...an-2016-a.html.
As far as baggage, etc. you might choose to change the flight from your BAEC Frequent Flyer Number after you are checked in - at the Admirals Club, or even at the gate (arriving early at the gate makes this easier for everyone). I can't imagine there would be a problem if you said you had changed your mind and now wanted to credit AA so you could fly and gain status on AA; they should be happy to help.