I'm not positive but I don't think the sunglass part comes out.
The entire thing can be removed by removing a single screw then pulling down on it I believe.
I know there are several pictures and a writeup of how to remove it somewhere around here.
I've taken mine out several times without breaking anything, so I don't think you're gonna have to replace stuff.
Search for overhead console or possibly homelink.
second post in this thread has pics: http://www.toyota-4runner.org/4th-gen-t4rs/85593-auto-dimming-mirror-install-w-pictures.html