Is there a way to empty the blacklisted area in the Plug-in Mgr ( OR delete the actual source files) so you can at least save all that HD space?? 
Follow the paths listed in the plugin manager in the blacklist, and delete the plugins you don’t want. That can be problematic with a few plugins that write info to the registry (in Windows) or elsewhere. You best option would be to use the uninstaller, and if your getting rid of VST2 versions and using the VST3, rerun the installer and just install the VST3 version.
iZotope plugins are a big example of plugins that the VST2 version gets blacklisted if the VST3 version is installed. That’s most of my blacklist.
This probably won’t free up tons of space. You can probably do better just running Disk Cleaner, and make sure you click the “Clean Up System files” icon to get rid of old Windows Update files - that usually frees up several Gb. Not sure what the equivalent program is on Mac if that’s what you’re using but you can Google “free up disk space on Mac” and find some help.
Sorry for the late reply…“SF” Thank you for your excellent advice!!