I would think that you would have to replace most of the front clip to update to the newer style. An even then there may be some slight changes in the styling that would not line up properly if you tried it. I know that when Nissan refreshed the Altima, you had to replace everything forward of the doors due to slight changes that affected the hood and the fenders too.
I think there are quite a few of us who prefer the original CX9 styling over the mid-cycle refreshed version. The later models do get the benefit of a much better Audio / Nav system, but they also get that damn goofy smiling grille.
The interiors seemed to have changed for the worse (IMHO) as well, with a lesser dash cluster, and the fact that they no longer have the ambient lighting in the cabin.
Beauty is in the eye of the beholder though, so I am sure that there are many who prefer the newer models over the older ones too.
I am anxious to see how the 2nd gen looks. I really like the CX5 and hope that the styling translates well on the larger CX9 platform. The new Takeri \ Mazda6 concept is hands down the best looking mid-size sedan I have ever seen. If the next-gen 6 really does look that, I may have to add another Mazda to my fleet sooner than I wanted to.