I know you can prune them and I have the same questions because mine are where they will eventually block the view.
However, I have learned one thing. When the straight, extremely fast growing, "water sprouts" shoot up above the rest of the growth, trim them two or three feet lower than the top of the bush. They will branch and then new growth will then be even with and thickest at the top of the bush, right where it will look most natural to the shape of the bush.