If the nomination of an agency or organization as provided in section 17b-267 is made by a group or association of providers of services, it shall not be binding on members of the group or association which notify the Commissioner of Social Services of their election not to be included in such nomination. Any provider may, upon such notice as may be specified in the agreement under section 17b-267, withdraw its nomination to receive payments through such agency or organization. Any provider which has withdrawn its nomination, and any group or association of providers which has not made a nomination, may elect to receive payments from any agency or organization which has entered into an agreement with the Commissioner of Social Services under section 17b-267 if the Commissioner of Social Services and such agency or organization agree to it.