Yeah Houston the only way that I know you can use the same Key Code is for both computers have the same guid (in your case both using the DL version or the CD) and both of you be behind a router that has the same IP connection, and NOT to be playing with punk buster.
As for changing the keys and your stats resetting, I'm almost 100% sure that if you change your Key Code that your stats and settings will remain the same and not change. In any case what you should do is make a backup of your profiles, that way if or when your shit does reset at any time you'll still have a backup profile to replace with it
You can find a How-To for the
back up Here
