Import and Update Users with Multiple Roles

Hello, is it possible to import a CSV and update roles for existing users with the selected default role, while maintaining their existing role/s (using Members Plugin).? For example, currently I have existing users with a role of “Street Team”, and want to import customers from a third party website. So the default role would be “CustomerB” and for existing users, I would want their existing roles to remaing, while appending the new role from the import. Currently, updating roles for existing users replaces the role.