adding a registration (vendor) to a specific grou

-- url of the page with the problem -- : www.biotoo.com/
-- HikaShop version -- : 2.3.2
-- HikaMarket version -- : 1.4.3
-- Joomla version -- : 3.3
-- PHP version -- : 5.4.30
-- Browser(s) name and version -- : Chrome latest

Hello

I would like to know how to force adding a registration (vendor) to a specific group.
For instance, I created a group "vendor" in order to show some menus only for the vendors.

I think the only possibility is to create a mass action when an user has been created.
* Filter user_vendor_id>0

Am i right ?

Thanks in advance