Read the link in my signature. If you install a ROM, you remain rooted... You just have to be rooted to have wireless tether, and it's an app... So you can download it again if you need to...
Be sure to read the "known issues" of a rom if listed in rom thread. Sometimes wireless tether doesn't work accordingly with certain roms or it may just work intermitently. Don't be afraid to ask for assistance here. There's WAY TOO MUCH help here to have your phone "messed up"..