The slaves themselves? Not at this time. Only the Shortstacks because the Player can produce a Woman with the Shortstacks modifiers.
I might make a small script if I can figure it out to give the player traits.
Edit: Just to let people know, the traits and chances are in the character files. If you only wanted to modify things so values are 'positive', just change the values in the general.trait file with a text editor. I'd keep a backup file though.
Edit 2: It is easy to start the game with a Player with any trait. It'll take you 2 files. I've added a small readme to hopefully help if you need it, and tried to comment things if you want to change things. This file only works on a new game, because I was being lazy. The file only gives the Player DeploymentCost: -1, because as of now, there was no way else to get the trait. Not that useful currently, though making Archers and Shortstacks Cost 1 is a benefit. Units (as of now) can't cost 0.