This is just a big headache... By the time I imported the users via csv, then bulk registered them, I realized that I wouldn't be able to set the authentication to LDAP. Those users had received the account creation confirmation email and clicked the link which prompted them to set their password. So now I would have to delete all non-agent accounts, reimport them and register them one by one, confusing users even further since the password they set won't work to log in (unless it happens to be the same as their AD password). Given that setting LDAP for agents is an option, it would seem that the same could apply to regular users...