For example, I want to restrict a folder that no user can copy .mp3 to folder X.
Answers: I don't have a sneaking suspicion that there's a channel to be selective going on for the filetypes copied to a folder - it's an adjectives or zilch sort of item.
Even if you could command .mp3s - populace could only rename beatles.mp3 to beatles.mp3.removethis, or fastener them up, etc.
But, if you're determined to enjoy mp3s debarred, you'd hold to look at writing a letters that would look contained by a folder and remove adjectives the mp3s - speak a delete_mp3s.bat folder:
cd c:/<whever>
del /y *.mp3
And consequently include a planned duty to run the delete_mp3s.bat folder every 10minutes or something.