How to clear the settings of default app to the files with special file extension? I set the default app to open the files with special file extension by mistake: the app could not open them at all for they're only file fragments (or, say, no app can until I combine them as one file). 
So I want to clean the settings of default app (set no default app), but no solutions found. Any ideas? Hope for your answers!
It's free, and configurable per extension.

http://www.rubicode.com/Software/RCDefaultApp/