Hi there! I'm wondering if its possible to use different FFN's for different segments on a single itinerary. I've seen people mention that you can have your FFN changed segment by segment at the gate or at check in for accrual purposes, but I would like to know if this is something that can be done beforehand, primarily for seat selection. Example would be MIA - LHR operated by AA and LHR - FCO operated by BA. I'm gold on AA and sapphire on AT, so I want to be able to choose MCE (at 24 hours) on the AA segment, and then choose preferred seats on BA. Thank you!