I have a friend that have replaced countless Gibson nuts. The issue is that the sides of the original nut are lacquered over. That finish has to be scored there (and on the headstock side) to remove the nut. If done wrong, yes, the finish can chip.
When you install the new brass nut, you have two options:
1. Fit the nut to be flush with the finish on the neck/binding. You new nut will not be finished over.
2. Make the nut undersized in width by a hair and build up lacquer on the ends to make it look stock. That’s a lot more work, with no benefits other than cosmetics.
My personally find Gibson factory nuts to be too high most of the time and like to cut them deeper as well. The trick is, of course, not to go too deep.