I don't know why you want to trim them, but you can.. If they are overgrown to the point that they are causing problems such as they have trouble walking, all you want to do is strip some of the excess off. You don't need to go all the way back to the quick. If you just trim them back some, not try to take them back all the way, they probably won't even bleed.
I've used a Dremel tool with those disks you use to cut metal. I just wrap the bird in a towel to keep it calm and trim them off. It usually doesn't get bloody at all, but it is probably a good idea to have a small amount of flour on hand in case it does bleed. You can stop the bleeding by just throwing a little flour on it.
As long as you don't hit the quick, which is at the base of the claw, the chicken will not react at all when you do it. It doesn't feel a thing, just like you trimming your fingernails.