"completely different" in this case means "parts aren't interchangeable", but not that basic principles or shapes would be different, for example, changing audi rear axle bushes for golf rear axle bushes or something like that.
As for way how to change bushes - there are at least three ways how to do that, and two of them requires axle removal. Easiest way is with special clamp and adaptors - as the audi rear axle bush is round, with even shape, such tool would require just unbolting and pulling down axle ends where bushes are, and with pneumatic gun, would simultaneously push out old bush and get in new one. However, it's unlikely to get hands on one...
Remaining two requires rear axle removal and use of common tools - the best one requires hydraulic press, if the axle could be placed in one - I think audi axle permitted that, but I'm not sure - axle of mk2 golf, for example, didn't allowed that, as there are some additional stuff welded to the axle that don't provide enough clearance. And so we got to the final option - old bushes could be burnt, or just cut out, shells cut with something [I used dremel], and new bushes pulled in with long M12 bolt and two nuts on it, but it required thick [approx 1 cm] metal plate with hole in it on the bush side, and something similar on the other side.