Any new rom updates for beast should be done with update.zip if you use nandroid you will again wipe everything. Update.zip should not wipe any of your apps. Now if you want to go back to stock you have different options depending on if you want to stay rooted or not. There are some posts nd Roms for doing it both ways on these forums.
With update.zip remember to select install and then select allow update.zip (or something like that) before updating. You will know if you miss it because you will get an error. Not a big deal if you forget since you can just go up, allow it and then install again. Once install is successful you just hit the top button one time and select reboot.