Update on this: I have contacted BA several times to enquire about this change (outbound change to SFO->LHR, different date). As others have helpfully indicated on here, it is indeed possible to change the original and destination as part of a "change" to a reservation/ticket.

However, some very odd things have happened regarding the pricing. Originally, I booked a "T", world traveler plus, fare in both directions - and the price came out to about $1500 total. When I check the same WTP/T fare today using my new origin airport (SFO), the fare comes to about $1300 - lower than the original.

Since the current new fare is lower than the original fare, I would expect to pay only the $275 change fee to change the outbound leg of the ticket. I have been quoted several high fares (latest before today was about $1200) to change the outbound leg. After a 3-day wait for a call back, they finally just now called and said that the fare difference is over $2000. This was, she said, after consultation with the "fare desk" - wow!

So now, I give up - I would like to cancel the original ticket and just buy a new one. If I cancel, I'll get about $300 in taxes back and lose the rest. I would like to dispute the refund amount - is there any way to contact the Refunds dept via email, and not have to play telephone tag again?

Thanks