No. Dark Arts policy is very strict about that one. If you are discovered to have multiple usernames all accounts will be deleted without warning. You may reregister, but if you are found in violation of this rule again, you will be permanently banned from these forums. It's in your best interest not to test this one out.
Sadly, a number of members have recently been discovered to have more than one account registered on your IP address. IP addresses that are not associated with AOL, Sympatico, or any other DSL/proxy service are those that come under investigation for possible double accounts.
If you want to change your username, just ask and have a good reason for it. If you have a sibling (preferably one that exists) and they want to join, please inform an admin before it happens so that both of your accounts are not deleted. If you forget your password and can't get back into your account, try the "forgot your password?" option instead of making a new account.