We've booked LHR-HKG and PEK-LHR for next year on a 241, but we're now planning to head more towards southern Asia rather than the north. This means that PEK isn't an ideal place to return from (since we're likely to be closer to BKK).

I've done a bit of searching, but I can't work out whether I can change the return (PEK-LHR) leg of the flight without cancelling the outbound. I seem to remember a thread suggesting cancellation was my only option, but I'd rather not lose the outbound A380 to HKG.

Is it possible to change the return leg only? Does it matter if there's a difference in Avios or taxes (assuming I'm happy to pay the difference)?