Use Property List Editor to edit plist files for free
Property List files, or more commonly known as plist files, are basically Mac application specific preference files. They contain information and settings for various applications and are usually in the easily identifiable format of com.developer.Application.plist and located within the /Library/Preferences/ directories.
You can edit these directly and very easily with Apple’s Property List Editor application. Property List Editor comes as part of Apple’s Developer Tools X Code package and is well worth downloading.
If for whatever reason you don’t want to download Apple’s XCode and Property List Editor app, you can try Pref Setter, which is another free plist editor solution.