- Create a new StandardUser (name it ex.Blah),
- Log in as this user and setup account as you want it to be for Guest,
- Log out,
- Log in as any administrator (for rootskipsudo),
- Execute those commands:
sudo rm -rf /Users/Blah/Library/Caches/*
sudo rm -rf /Users/Blah/Library/Keychains/login.keychain
sudo rm -rf /Users/Blah/Library/Preferences/SDMHelpData