You can bring forth files (edit data, kit pngs, emblems) from PES 2011 to PES 2012 via the 'Import Prequel' function. However, the prequel import also brings some distortions that make the file less than ideal.
I had orientated the 'edit data' for people who did their own prequel imports on 2012, to clean up MLS & NASL specifically. See the last few pages of this thread for details and the d/l links, if interested. If you wanted to use those files, you'd basically do your own prequel import and then delete the edit data, replacing it with one of my orientated edit datas. (I posted one file for the default game and another after the first round of DLC. A further complicating factor, though: since then, a second round of DLC has dropped.)
Another thing I'd point out is that PES 2012 has a new import/export function specifically for clubs that can be pretty useful -- and fcpappin is getting close to releasing an import pack for PES 2012 with relatively up-to-date MLS sides, including the expansion Montreal Impact and some of the new kits for 2012. You might want to keep an eye on that, too, if you pick up the game:
http://www.pesgaming.com/showthread.php?t=88692