why not just let the know-it-alls do what they want? if they're as good as they think they are, they won't have a problem completing their course requirements. if not, maybe when they start failing they'll reconsider their position and adopt some modesty.no need to struggle with the students!
Why don't you politely suggest that they leave and get a job while they still know everything?
If you already play piano you could probably proficiency out of any piano requirements. However, the class piano course is different than what I had for regular lessons. Class piano included improv and transposition.
As a music major, with piano as a required second instrument?