Originally Posted by
EnvoyBoy
You probably won't loose your outbound preferred seat but you may very well loose the return seat when a computer sweep bumps you out. I can confirm from personal experience that you WILL immediately loose any upgrade you got based on your US status.
Good point about losing the upgrade, but the OP seems to be referring only to preferred coach seating.
As for the comuter sweep, what if, upon landing after the outbound flight, the OP called the DM number and told them to apply his DM number to the return flight? That should hold his preferred seating assignment. Then the OP would have the option on the day of his return flight to change the FF number to UA's if he so desires.