I'm installing it now. I was on .904, but reverting a stock .904 system to .902 is simple - using moto-fastboot all you need to do is flash both boot.img and system.img from the stock .902 FXZ, and your stock phone is now .902 again.
1) Do not need to unroot.
2) *DO* need to make sure your stock system in pure stock - with bloat and all. Debloating *may* cause the update to fail.