Anything you hang on a barrel, and I am designing .300 win mag clamp on muzzle brakes right now, impacts the harmonics, the drop and obviously, the resulting POI. How much depends on the brake, specifically the weight, muzzle diameter, number and sizes of the ports and direction of same.
How much it impacts the POI which is all I would be worried about as long as it is consistent, varies by brake as well.