If you do rename, does it make all the current accounts with Administrator access unable to get to the server, do they have to be changed to the new name (like what would happen if you changed a users login name)?
Do not confuse the administrator account with the administrator group. The group is what provides the permissions. You can delete or rename the account with no ill effects to anyone else.
Also, the author mentions creating a "bait" "Administrator" account (if you do rename the "Administrator" account), give it an obscure password, disable the account, and make the account a member of the "Guest" group only. That way, a hacker will find the Admin account and not be able to go anywhere even if they figure out the password.
I've always thought this to be a waste of time. This might stall a decent hacker for maybe...20 seconds.