I went to the Ogden Office. The mods required are turn signals, a horn, a license plate light, rear view mirrors on both sides. It has to have a safety inspection by someone who can inspect motorcycles and has requested ATV safety added to their motorcycle certification.
You will be charged for both off road and on road fees to register.
The registration will be at you home county, you may not be able to operate in you home area but will be ok in the countys that are approved.
If you have questions see SB181S01--Off- highway Use on Public Highways. from the Utah Gov. web site.