Hi Anthony,
Group registrations are considered an individual/standalone registrations. And hence you will only be able to cancel/modify a group member's registration if you have the registration confirmation number and their email address and you login to the registration as them.
Group leaders will get the above mentioned information via email when registering the group members.
Regards,
Khushbu Gupta
Associate Quality Lead - Quality Team
------------------------------
Khushbu Gupta
CventUnited States
------------------------------