I've tried clicking on everything in the settler screen and the only thing that gives me any control over their stats is the randomize button so I spend 5 minutes just trying to get the back-stories that I want to appear. In my second base I must have clicked 100 times trying to get a slave/settler, but there are only 35 combinations of back-stories. I don't mind the back-stories affecting their skills but at least let me choose them without relying on randomization.