In our specific case, we want to allow players to interact with a waystone so they can teleport away from claimed areas they do not own/have access to, in the same way we can allow them to access doors/chests/barrels/etc. The block types should probably be able to go on a list somewhere though, so other servers can put specific blocks on there, whether it is waystones/post boxes/other mod added blocks doesn't really matter. Just the ability to grant use access.

You can do that in the main config file openpartiesandclaims-server.toml. The option you're probably interested in is forcedBlockProtectionExceptionList.