Is this possible?

I am waitlisted for GPU on 869 SFO to HKG tomorrow. I set an ExpertFlyer alert and see that R/RN inventory is now 1, however I haven't cleared. Happens commonly, I know.

I am not checked in due to some passport verification issue, and they are already clearing people for upgrades, while I am not even allowed in the cue until I check in at the airport.

If I were outside of 24 hours, I would call in to have the upgrade confirmed or cancel and reapply the upgrade if necessary. However within 24 hours of departure, I am sure the agent would not confirm the upgrade but rather would tell me to wait for waitlist. In that case, could I take the backup route of cancelling and reapplying the GPU? I recall that back in March, it became impossible or very difficult to apply GPUs within 24 hours of departure - a pmCO policy I gather. Is it still hard to apply GPUs within 24 hours of departure?

Thanks in advance for advice - I assume despite paying $2300 for this ticket plus a $300 change fee, I'll be stuck in economy, but I'd love to prove myself wrong.