I've never used a symbian, but in my experience most exploits (especially replacing root certs on a phone) do not use the screen. So if your screen gets damaged, you hook the phone to the computer, reverse changes, and send it in for repair. Then restore changes when you get the phone back.

Yeah it's a pain, but that's the price you pay for 'added features' like this.

That said, I don't think you will be able to forge a key, otherwise I would be signing certs all day long as verisign.