bbf, I just commented on this in the other thread about the '10 Fusion but probably should have put it here. I see that the rear of the Fusion is much better looking than ours. I love those taillights, but it looks like the bumper will obviously be different. Do you or does anyone know if the rear body and trunk sizes will be identical to the 06-09, enabling me to just buy a rear bumper and set of rear taillights and swap 1-for-1?
Hi thereisnospoon.

The sizes and cuts (at the fender/trunk lines) look to be the same. I just downloaded a few shots of the 2010 rear end to compare them to the present models. At least as far as could be seen in the pictures, all of the peripheral fender cut lines and trunk cut lines look the same. Assuming that the bolt up and fastening points for the tail lights and bumpers are the same for the 2006 through 2009's and the new 2010's (they likely may be), it should be a relatively simple (but expensive swap). I say expensive because by the time you buy two tail lights and a bumper, then have the bumper professionally painted, it will run a few bucks.
Thinking out loud now: Other than the cost, the only other possible "problem" I see (and it may not be a problem to you), is a styling consideration. The character lines and indentations on the 2010 trunk lid are
completely different than the 2006-2009 models. If you look closely, on the 2010 the new character lines and indentations on the rear of the trunk lid match up and flow with the character lines and indentations in the new tail lights. And while the 2006-2009 tail lights had smooth covers, the 2010 does not. They have indentations and character lines that flow into and match those in the rear of the trunk lid.
From the rear of the 2010, the character lines almost resemble a wing that stretches across the trunk into the tail lights, the tips of the wing on each side being the clear/white back-up lights. I am not too sure how the new tail lights will flow with the rear of the old trunk lid, which only has the large center indentation surrounding the license plate area (no wings).
Just take a close look at some pictures of the rear of a 2006-2009 and compare them to photos of the 2010 rear end. Just be sure you can see the trunk/tail light character lines and indentations in both shots. It may be something that many people will not notice or mind. All just a matter of personal taste See what you think.
Let us know what your thoughts are.
I would also recommend the following: Once the 2010's have arrived at your local Dealer, take a drive down in your Fusion and park right next to one. Compare the cut lines on both cars. Compare the attachment points of the fasteners. Take a good look in person as to whether you think the modification is really worth it. It is always hard to tell in pictures exactly how the lines of a car actually flow. Besides, the parts would not even normally be available for purchase until sometime after the 2010's are on sale anyway, so you have some time.
Good luck.