In the Users Rights Assignment, they are either given to a user or group, or not given. They cannot be enabled, disabled, or not set (like some security options can be). A user either has the assignment or does not have it. Therefore, if you had to be assigned that right first, then you would never be able to enabled it. I'm guessing all the Users Rights Assignments listed are part of the token, whether disabled or enabled. Otherwise I don't think you would ever be able to enable a Users Rights Assignment.