Is this a RT? If so, I'd worry about the DL rule that you can't change a FF number in the middle of a trip. My impression is that DL is concerned about someone getting elite benefits from one FF program while crediting to another, but of course the same issue can arise if different segments cannot be credited to the same program.

An alternative would be to not use any FF number at the time of travel and then retrocredit, but this would be a big hassle.