I have the return portion of a ticket in paid economy W, YVR-SFO-LHR, with a waitlisted GPU applied, and a one hour connection at SFO. I would like to fly a couple hours earlier on the YVR-SFO leg to make a longer connection.
If the international portion SFO-LHR clears into PZ before the day, can I SDC the YVR-SFO portion only and still keep the upgrade for SFO-LHR intact? Do I need to call an agent, and not use the app? Does it make a difference to the answer whether the YVR-SFO portion also cleared upgrade before the day? (I think I read that in any case I lose the YVR-SFO confirmed/waitlist upgrade if I SDC the YVR-SFO flight unless the new flight has PZ>0).