Replaces the type and the notes of one of the customer's relationships ('notes' is cleared when omitted). Only this customer's side of the relationship changes: the opposite relationship on the related customer is left as is. The related customers themselves are not changed. Returns the updated customer. Errors: 400 with error code 40001 when 'type' is missing or invalid; 404 when the customer or the relationship does not exist; 400 with error code 40000 when the caller may not access the customer.