Any experience with doing a SDC after having done an eupgrade on a latitude or flexible premium fare? Can I do a SDC, then successfully re-upgrade on the SDC, assuming there is availability.

I booked a summer flight, not knowing that the flight an hour earlier is a 763 with pods. Currently on an A320 flight. Already e-upgraded on a B fare as part of a premium economy O booking for the 2nd leg.

Bought when O fare was $700/RT cheaper, so reluctant to cancel and redo booking.