[kh99]

Do you mean you want to add another group as a secondary user group? You could try creating a promotion (under the Usergroup menu in the adminCP) for Registered Users. Set "Days Registered" to 0, "Promotion Strategy" to Join Date, "Promotion Type" to Additional, and "Move User to Usergroup" to the additional group. Then go to the Scheduled Task Manager, find the User Promotions task, and press "Run Now". The one problem with this is that a promotion only applies to one starting usergroup, so you might have to repeat the above if you want to do it for more that just "Registered Users".

Another problem with this is that when a new user registers, they may have to wait up to an hour to be added to the new group. Or maybe what you could do is to use the promotion just as a way of getting the current users there, then remove it and come up with another way to get new users added.