Originally Posted by
erickliu
SDCs made in the app will maintain upgrades, unlike agents who can only change you onto the originally booked fare class (or push an upgrade if available as well)
This is only true for GS (and, Gold or Silver passengers that cleared into RN before checkin, but I'm confident that's an error and it could be removed at any point). Anyone else on an upgrade -- instrument-supported or CPU -- will wind up back in coach after an SDC.