Ozzie Smith '92 is now an A/A fielder. In numbers, that's 11/11.
So, here's the way I think it works. In 2009, he's an 11/11 in a 10-world and in 1915, he's an 11/11 in, say, a 7 world. This doesn't mean that he drops from 11/11 to 8/8, it means that he retains the same relationship to a 12/12 or a 9/9 that he had in 1992, whether he's in 2009 or 1915.
He'll make more errors in the 1915 context, but will still be better by some percentage than the 9/9 fielder in the same context.
Having said that, there is really not a world of difference between an 11/11 and a 9/9, so I expect that we're all going to notice the difference between the 2009 context and 1915 more than the difference between individual players.
In the beginning of this post-update world, we're all going to be reacting initially to small statistical samples. Sqwaks will be forthcoming from those who have bad luck -- but it's going to take a lot more games to see how this plays out.
dtownlove may be right: the best approach may be to pretend this update never happened...