If you can't see over or around it, it may be an issue. The statute that would probably apply would be regarding preventing collisions.

Sec. 15-131. Rules for preventing collisions.
(7) The operator of a vessel shall at all times maintain a proper lookout required by the ordinary practice of seamen and by the special circumstances of the case.

If you modify the boat and don't have an accident, no problem. But, if you modify the boat and have an accident because you could not see an obstruction or another boat then you did not (were not able to) maintain a proper lookout.

There may be US Coast Guard regulations too, you would need to check with them.