Now that there is an update to Gramps 5.1.3 on the Windoze PortableApps, it might be possible to start using that for my documentation & bug testing needs!
It will still require some experimenting to determine if the User Directory is also sufficiently isolated when using that installation. (I hope. I hope!)[it does] That would allow using the settings I REALLY want instead of just the stuff that is easy to revert.