Possible "undo"
No matter how you did it, system user interface preferences are stored in com.apple.systemui.com (I think that's the full name) which you will find in HD/Users/YourUserName/Library/Preferences
Move the plist file (not com.apple.system.com - it has to reference the user interface or "ui") to your Desktop
Restart. This will create a new plist file in Preferences.
If all is well, you can Trash the ui plist file you placed on the Desktop.