Based on your first question -- I think you would run into problems with the ultimate crediting. I dont think the AA computers are set up to have two different FF numbers in the system. My guess would be that whatever FF number you used on the 1st leg would apply to the second leg. You would have to go back to AA and tell them you wanted it credited differently, but I can imagine that would be a nightmare.

For your second question, I think you would be OK on a 1 day trip -- since it is the return portion -- but I would call and make sure.

--Jim