Yeah, I kept digging and found a way. Each company has it's own set of client groups. You look in client_groups for the id of the group you want the client to switch to, based on the company_id field. Then you run a SQL query to update the client_group_id inside the clients table to reflect the new company's group. Now you're all switched over!!! Could be a nightmare with enough records, or too many groups but... I managed.
