Deleting Default Logon Account settings for old users

I am trying to cleanup a Backup Exec install that was set to use a user's own domain account as the System Logon Account.  The problem I am running in to is that it was set as the default account for multiple users.  Is there a way to delete those logon associations so that I can delete the System Logon Account and create a new one without having to uninstall and reinstall Backp Exec from scratch?