Originally Posted by
pedro colizzle
... Is it possible to use my United FF# for the outbound portion of a round trip, but switch to a different FF# (say, US Air) for the return? ...
yes, but the outcome may not be want you desire depending on the gap.
Recent reports suggest the FF in the record at time of posting, not time of flight, is determining the account. So if the outbound posts before your return flight, things should work out. This means there needs to 3,4,5 day gap.
A shorter gap
may lead to an unexpected outcome.