I replaced the expansion valve in a 560SL. Like has been said, it is not easy but can be done. Just need big wrenches and a lot of patience. I worked through the cluster hole and from underneath. I did not remove anything except the cluster and lower cover panel. The lines were real tight, but once they cracked loose, it was not a problem. I was replacing the expansion valve anyway, so any damage I might do to the valve would not have been a problem. There are copper washers that seal the connections that you will need. I would not splice the line, as it is high pressure and you might end up with leaks or worse.

Concerning the vacuum pods, is the defroster flap pod accessible from the instrument cluster hole? I just found out I need to replace it. The manual says to remove the console and dash, but I will do whatever it takes not to do that. Sounds like big trouble. From pictures in the manual, it looks like it might very well be accessible, though probably not easily.