Updates on what I found out on-site when I went to exchange our expired pre-COVID tickets. The crux of the issue, as noted above, is that two groups are involved, Guest Relations and Ticketing. GR can move reservations, but cannot exchange expired tickets. Ticketing can re-issue tickets, but cannot touch reservations. Ticketing is also frustrated that the web team hasn't fixed the problem of letting people make reservations with expired unused tickets.
If you only have reservations on expired tickets, the problem is that once Ticketing voids your old tickets in order to re-issue them you lose the reservations. So if you have expired tickets, the only way to keep from ending up with two sets of tickets would be:
1) Buy a new returnable set. Make reservations with those tickets.
2) Visit a ticket booth at DL and have them re-issue your old expired tickets.
3) Visit the Guest Relations booth outside of the parks and have them transfer your reservations from your returnable tickets to your newly re-issued tickets.
4) Return the returnable tickets used to initially make the reservations.