I want to say Sonarr has a regex renaming feature, but I may just be making that up as I'm not looking at my instance right now. Doing whatever renaming based on a pattern would be preferable during the download phase in order to keep the metadata of each service clean.
Failing that, if you have a predictable list of release group strings you want removed from filenames, a one liner with sed or similar would take care of this. You'd then break the known locations of these files by any service tracking them of course, but they will eventually be reindexed.