There are the experimental rules called the power in the stones which appeared in TC 15 page 32. There is a D66 table for random mutations, some beneficial and some crippling. You can only get them from the using analyzed wyrdstones and not be chosen by possessed warbands as usual I think the table includes some of those official ones though.
I call this article official enough to use -- the rewards are offset by the cost and potential hazards of use.