Save all your important files to dropbox or w.e and wipe your drive / reinstall windows. IMO it just seems easier, faster and more efficient. all my important files are already in the cloud / saved to a separate hard drive.
To reinstall system menu find the .wad from Modmii and install with YAWMM.
Make sure you have the IOS for each system menu.
4.1 = IOS60
4.2 = IOS70
4.3 = IOS80
Priiloader will save you from bricks caused by themes. Priiloader will only stop working if you reinstall the system menu or uninstall the system menu IOS.