In-program method to Revert to Factory Settings
The vast majority of errors are solved by following the steps to revert to factory settings from the command line. However, many users are not familiar with the command line and may struggle to do this, especially on Windows or Mac systems. (MuseScore is automatically added to the users PATH environment variable on Linux, but not Windows of Mac, so more commands are necessary than a simple "mscore -F".) Since reverting is actually a relatively common task (I have had to do it after every MuseScore upgrade) I think it would make sense to make it available in the GUI.
A "Revert to factory settings" button could be added to Help -> About. This would trigger a warning dialog, followed by an "Are you sure" type message to avoid accidental usage.
The code could potentially be as simple as restarting MuseScore with the "-F" option.