I made this conversion about the same time I did the one with the horns. I don't know if I've used this model before but I have tried out fangs I think before. It helps when you foul, so fangs plus dirty player is the ultimate fouling model. However I've moved away from fouling for two reasons. One rule changes have made it more likely you will get caught and thrown out of the game and two I want to score and encourage my opponent to score. Often I play teams that just try to beat my team up and win one nothing. This doesn't always work but the Skaven are brittle and I try to minimize the number of armor roles I have to agonize through. That said stashing a Skaven with dirty player and fangs on your roster could prove useful in getting rid of that really annoying opposing player.
One conversion I want to do, next time I play in a Bloodbowl league is a Skaven with stunty. Several times I have had Skaven loose one strength. And with the addition of big guys again to a Skaven team it is not unconceiveable that you could take an injured Skaven and mutate him to have stunty, right stuff, and still move really fast. You would also of course need a Rat Ogre with throw teammate. Last time I looked at the rules this was possible but it would take a lucky combination of rolls to pull off.