Much like champignon, my experience with BA awards with AS mile (Usually in Business or First) is similar. However, if the change is due to BAs schedule, even if they have not had award space in the cabin I was originally booked, the Alaska Partner Desk will request BA to release additional award seats and it has always been granted. This happened to me recently on a trip to Prague (EUG-SEA-LHR-PRG) as the SEA-LHR leg I was booked on was eliminated. They moved me to the only other flight operated by BA which had no award space until they asked BA for it. Same with the leg from LHR to PRG.