You probably also need to edit the values in basic.php which is inside /helpers in admin components. However I don't think the plugin fully knows how to deal with this yet as it still waits for MailChimp to tell it the registration is successful and update the list, but since that never happens, the list does not appear to get updated. At least that's what I think I'm seeing. You can still update your lists again from MailChimp and see the change though, and no confirmation email is sent once you set double optin to false in basic.php.

- Oshyan