"Network admin: stop being such an ass."
I'm not in your situation, but it seems to me that the exact same message could be written on a piece of paper, signed "concerned students," and placed on his desk.

Don't gratuitously destroy property when there's a socially accepted way to deliver your message.

Do you think defacing your school's page will somehow lessen your admin's crackdowns on websites? Use some common sense, and realize that your actions will not solve the problem you're trying to solve (assuming you actually want to decrease the number of unfair things your admin is doing).