Ideally yes, it can be done with it on but it a bit of a nightmare and you will need a special tool. Easiest way I done it was to remove the calipers then drop the axle. I set fire to the original bushes to burn out the rubber then using a hacksaw I cut a slit in the bush casings then they just chapped out with a chisel. Then just clean up the inner surface with some sand paper, bit of grease, then powerflex bushes just slot in place.
