The front overhead cluster has a 12 wire connector to it, but 3 of those wires are "missing" from my loom (I do not have the front map lights). I think those 3 might be for the map lights, I haven't tried it, and it's £63 for a cluster which since it is coming from Germany my dealer would not refund if it doesn't fit.
The rear cluster (also non-map light) has only two wires going into it, and they are only live when the interior light is on. Thus, the rear cluster hasn't got the permanent live required for rear map lights. Hence, again, a different loom is needed.
It seems it is not just a straight swap, unless I am missing something
BTW the second two pin connector on the rear cluster is for the LED Welcome Lights, I had hoped for that to be a permanent live but as you will see in my other thread with the photos I took (
http://f20.1addicts.com/forums/showthread.php?t=720656) it is just for two white SMD LEDs.
Summary is I think it's a not possible, both front and rear map lights, without ordering the Extended Lighting pack.