How to randomly assign one of three traits to every sim

I am very new to modding (as in I started a few days ago and looked up a bunch of tutorials) and I'm trying to figure out how to randomly assign one of three different hidden traits to every single sim automatically (Let me know if this was the wrong place to post). I started using mod constructer by Zerbu and would really prefer to only use that application if at all possible since I don't know how to use anything else. I would really appreciate any help!