OP, if you haven't already, I will highly recommend that you got a subscription to ExpertFlyer, especially for the few days before departure. Set up an alert to monitor C availability, and when you get an email, immediately call the EXP desk to ask for upgrade.

Calling during the day of departure may allow you to skip the waitlist and grab the seats (AA's day of departure waitlist processing runs very infrequently, and possibly not at all during the last few hours before departure, making it possible that you may be able to grab a seat outside of the waitlist).

The EXP desk most likely cannot reissue your ticket, but you would have confirmed the seat, at which point your upgrade is secured. To be safe, you can plan on arriving early at the gate to make sure that your upgrade finishes processing properly.

I haven't done this in PVG, but I had an experience before upgrading someone without status out of NRT. They have already started their journey into NRT. I saw the C seat released and called the EXP desk. The upgrade was confirmed immediately, and the passenger only had to wait until boarding to get the new boarding pass. My guess is that my timely call allowed her to skip the waitlist.