Changing pitch will not change point of impact; unless as a result of changing the pitch, it changes where you place the recoil pad on you shoulder and as a result of this change your sight picture is altered.
Think of it this way. If you change the pitch on a rifle, will it affect the point of impact? No, the sights determine the point of impact.
On a shotgun the placement of the shooting eye in relation to the rib determines the point of impact. If and only if the change in pitch changes the position of the eye will the point of impact be changed.
With a straight Monte Carlo stock a change in pitch could not have a very significant impact as any change in eye position will be minimal as the comb is straight and has the same drop at all points.
The potential change with a skeet or field stock "could" be more variable as their combs slope to the rear. A change in pitch that results in the eye moving forward on the stock will result in higher point of impact. A change in pitch that results in the eye moving rearward on the stock will result in lower point of impact.