That's quite the thread necromancy.
Role preference changes when a slave gives(increase) or takes(decrease) any of the following punishing actions(copied from the code): ['spanking','whipping','nippleclap','clitclap','nosehook','mashshow','facesit','afacesit','grovel']
The change is small per action but adds up quickly with a few continuous actions, just watch out for stress build up. Also note that elves will have their role preference overwritten by their confidence at the end of the day.