Changing the aft cabin air conditioning in the 54 didn't pose any major difficulties for me. The new Climma compact 9000 has exactly the same dimensions and the same connections in the same places. In the aft cabin, you have to remove the wooden panel where there is the air inlet opening (there are 4 wood screws to remove). Then you have to remove the electrical connections as well as the water pipes. Then you have to remove the fixings to the floor (4 wood screws to be removed blindly). The unit can then be removed as a whole without any disassembly (I did this without scratching the woodwork). For the installation of the new unit, it is the reverse procedure.
it was a bit more difficult for the saloon because the new Climma 12000 is bigger than the original.