I have business class BKK-NRT-SEA-DEN booked JAL. First class space opened up on NRT-SFO that I would like to switch to. I called and asked the NRT-SEA to be switched to NRT-SFO and I will buy a separate ticket to get back to DEN.
I called and the agent spent ~20 minutes with the international desk and they came back and said it wasn't possible. Is this a HUCA situation or is this breaking a routing rule and not possible to do?