Bringing this thread back because I finally got to chat to BA about it. BA said that it's not possible to rebook me on a non-BA operated flight although it's a pure cash booking. HUCA?
My flight was the LHR-HEL 11.10 flight, moved me to 07:55 and I'm trying to rebook to 10:20 or 13:50 AY codeshare. Return flight has been changed from 17:00 to 13:50!!! This trip has been an absolute nightmare so far, my AY flights all had schedule changes as well so I had to reroute IVL-HEL-LHR to RVN-HEL-LHR and the day after my AY rebooking BA decides to do this to me.....