This is an obvious trick that I didn't think of until today. I didn't find it with a search, so it might be helpful to other Roll20 users. I'm playing Strahd and it seems like everything adjusts my HP maximum. I had added a HP Adjust item to the Feats & Traits box to keep track. Today the light bulb flickered on over my head and I typed [[26-3]] into the Hit Point Maximum field on my character sheet. It worked. I'll probably still keep the item in Feats & Traits so I know where the adjustment came from and how/when to get rid of it. But now I have another way to keep track of my base max. This will probably also work with Heroism.