Originally Posted by Nothinman
I'm sure you could do it by setting permissions on the appropriate keys, under HKCR IIRC, but it's not just a single key so you'll have to do some reading on how Windows handles file type associations.
Cool, I can see how that would work. One could even write a program to unlock those keys (i.e. set appropriate permissions) before installing an app that's allowed to make a change, and then locking them again.
I'm adding this to my potential apps-to-write list