To make the import of already existing users easier a new function is available in Group - group Setup - Basics.
This function "Ignore mandatory fields in the group import of exisiting users" will do following
1. Visitors already in the system will be shown on a green background
2. Import will ignore mandatory fields for existing users
Also a new UI ressource is available for additional info when this setting is activated "lblIgnoreMandatoryFields_txt".