If I were doing it, I would cut the brake off and have the barrel recrowned.  I don't think a 12.5 inch barrel would be appreciably louder than a 14 inch barrel.  In addition to the point about the T/C warranty, also keep in mind that nonfactory barrel modifications most of the time hurt resale value.  Also, brakes aren't actually louder, they just direct the sound in a different direction that's more troublesome to the shooter.