Updates one or more recipients on a document that has already been sent. Only recipients who have not started signing may be updated. Recipient IDs must be retrieved from the Get Document response. Allowed document statuses: sent, viewed, pending, bounced. For non-embedded documents, updated recipients will receive a new notification email. For embedded signing documents, email behavior follows each recipient's send_email setting. This endpoint does not support changing a recipient's delivery_method or phone_number; SMS delivery settings are set when the document is created.