Well I used Blubb1337's hardly an hour ago and it worked fine.
I launched it, launched MW2, went to barracks, and edited my stats. Made a few new custom classes, exited trainer, exited MW2, et voilá! :P
Try that or try instead of custom classes playing a game or two after setting your stats (be sure to exit the trainer first though to be safer).
As for copying stats from one account to another, as far as I know EAM can do that, however I've never tried it so I can't say how or how well it works.
Hope that helps.