It can definitely be done, as I have done it, but the ARB needs removing from the car to do so. Once off the car, separate the clamp that holds the bush by drilling the underside of the captive nut, or some cutting, its quite easy and obvious once off the car.... Once done, fit new bush around ARB, refit clamp around the bush, then refit to car. It can be a bit fiddly but if you press the two sides of the clamp together, they should stay together pretty well whilst you get the ARB back in place.