Thank you for your comments, a few things:

(i) I've read that cellulose acetate becomes brittle in sub-freezing temperatures. So while the freezer would slow the chemical breakdown to a crawl, it causes harm as well. I believe the fridge will do nicely for my purposes.

(ii) Cellulose acetate breaks down via hydrolysis, which basically means water/moisture needs to be present. Low temperature slows down this process, but protecting the tokens from moisture seems key. Oil could probably work, but it would be a pain to clean my set for play. So instead of oil I will use (car) wax. The only thing I'm worried about is that normally good ventilation is recommended, so that the released acetic acid may escape. The wax might trap it, but then again if there is no moisture because the wax, then (next to?) no acetic acid should get released either..? Not sure but makes sense inside my head.

(iii) It is important to store the tokens correctly before they start deteriorating and not wait until the process has started. This will drastically improve their longevity.

Interesting stuff.