Thanks for sharing a nice little release.
In review of the code, one step you didn't mention was that, if using a custom group name that isn't superadmin, admin, or user, the person who uses this will have to open the file manually (in notepad or other text editor) and verify the groups table has, and if not, edit manually, the groups they use and adjust the speed/healths if wanted.
There is no console command to modify real-time. (That would be a great addition)
Additionally, this has no reliance whatsoever on ULib or ULX.
It's 100% Gmod lua. (Which is fine, but the name you gave the release made me think it was going to have ulx console commands to change speed/health during server run)