It is not as straight forward when you are trying to manipulate the SecurityAssist implementation in PowerCMS. The rule that is used to protect the pages in the admin area is called Administrator and is defined as the session variable $_SESSION['AdminLogin'] being equal to the $GLOBALS['WAGLOBAL_Admin_Password'] value.
You can continue to make use of this rule, or you can craft your own rules and get rid of these. If you are going to be using Security Assist extensively it might make sense to do it like this instead. This way you can have complete control over the access rules and how they are constructed. I'm including a screen shot of the Administrator rule in the rules interface so you can see how it is setup.