I have three different Actions for this.
One auto levels each channel independantly, then backs off to 10% using the edit fade command. One does the same thing but only backs off to 20%, and the third backs it off to 30%.
It does indeed alter the normals when you change the RGB, but sometimes you want that, and it makes it read better in game. This works much better on organic stuff, I always leave my mechanical stuff as is, other than fixing errors.