Assign requests only to support groups with the technician field greyed out.
Make use of Field and Form rules to allow a technician to only assign a ticket to a support group and grey out the technician field while assigning requests
A third-party technician should not be enabled to assign requests to certain technicians only assigning a request to a support-group
To apply to all technicians who should be able to only assign to support groups.
To apply to specific technicians who should be able to only assign to support groups.
Final result
