Nope, boiling won't hurt them. Like was said. Also just be sure the horns are out of reach of dogs, and raccoons, if you leave them out in the sun. They come out pretty easy, but you might want to rinse, and bleach the inside a bit, as it is a bit rank. You could rinse, and boil for a couple of minutes. Also boiling makes scraping with a piece of glass a lot easier. When I was a kid, I used to go down to the local butcher shop, that butchered their own cows, and get the cow horns. We did like Eddie said, and just tied them to trees,with the sawed off end down, to drain, and facilitate the flies doing their thing with laying maggots in them. Not quite a week, they are ready to shake the bone out. Then clean the inside, and boil, and then scrape, and sand, and polish.
Wayne