Jim, the mailing list stripped the attachment. You will need to either give a link to it or send it to him offlist.
André wrote:
and switch about the same number of users from a group to another group?
I guess you are changing all users from a group to another? That would be easy to do with an sql query: UPDATE user_groups SET ug_group='newgroup' WHERE ug_group='oldgroup';
Adding all users recently registered to a group should be easy, too (although adding the option to Mass User Import seems the way to go).
INSERT INTO user_groups (ug_user, ug_group) SELECT user_id, 'newgroup' from user WHERE user_registration >= '20101014030405';
Where 20101014030405 means: all users registered since 2010-10-14 03:04:05