Somewhat related, not sure where to post - so will add question here.

If I have a multi-segment flight with the first segment on UA and following on NH, can I use different FF numbers for UA and NH?
I.e. - can I put my UA number on the reservation, fly the first segment, and then change to another FF number for the rest of the trip?
Does not seem like the UA site will let me do this? Or is this a question for the NH forum?