Bro, if you change your name to a name that already exists in the EF database, your karma and PM's will not carry over. If that happens, I believe that only the administrator can remedy the situation. DO NOT keep changing your name and messing with stuff... it only makes the admin's job more difficult and decreases the likelihood of getting things fixed quickly.
If you're having a problem, DO NOT make a post on chat or anywhere else here -- that's NOT how things get fixed, and the admins don't like members to handle the situation in this manner -- there's already established procedures for members to get account fixes. PM an administrator, ask a moderator, file a support ticke... and be patient. At the bottom of the main forum page you'll see this: EliteFitness.com Bodybuilding Forums Statistics: Members: 140,615. Take a wild guess how fun that is for the admin going into the database and doing this for people, lol.
For anyone thinking of changing their name, I strongly suggest doing a Platinum search for the new username you want in order to make sure that it doesn't already exist. This appears to be the biggest problem with the name change feature. Also, MAKE SURE YOUR EMAIL ADDRESS IS VALID AND CURRENT!
HTH