PSA: I found a use for my certificate that expires in about 10 days but I needed to add more points. The hotel now needs fewer points than when I booked.

It was pretty easy to just go in there and modify the reservation to the same day to get it re-priced. On the account activities, it processed as a refund of the entire original amount and a charge of the new amount but it did not show up right away (even after I logged off and logged back on).