I am in a similar situation since I bought a pre-06 facelift X3 3.0i for my wife and plan to retro-fit a M-Sport rear bumper. This seems to be straightforward, but some additional parts will need to be ordered to mount it (e.g., center bumper mount and loading sill). You can see a parts diagram here:

RealOEM.com * BMW E83 X3 2.5i M REAR BUMPER TRIM

I plan to keep the matte black "trunk lid finisher". Here is the M trunk lid finisher:

RealOEM.com * BMW E83 X3 2.5i M trunk lid cover

The 2007-2010 X3s do not use the larger finisher like on the 2006 model, so it should be fine. I could always paint it to match the body color someday.