There is a bit of divided opinion about this on the forum, but fitted them on my 800GS 12 months ago and didn't replace the brake line. As long as you don't tilt the risers back too far and you loosen the handlebar clamps on the brake assembly and roll these the other way, it will be fine.
Once you have them fitted, just check by swinging the bars full lock in both directions and make sure the brake line is not restricting movement or is too strained.
These made all the difference to riding in comfort for me, on and off road.