What happens to the rackets balance when an overgrip is added to the racket? -less head heavy? -more head heavy? -more balanced?
I would be inclined to say slighty less head heavy, but does not seem by much. I've not heard anyone say that it effects the balance. The overgrip itself is very light and it is at bottom of racket away from the head where small differences would be more significant.
I would say it is negligible since it is at the grip point. A heavier string would cause a much greater shift in balance. Of course the end result depends on what balance you started off with.
It would change the balance to (for stats purposes) slightly head lighter than it was. But on feeling there would be no difference, as you would be gripping at that point probably higher than some of the grip.