Nothing in this chapter may be held to diminish the constitutional rights of any person or to limit or repeal additional requirements imposed by statute or otherwise recognized by law. Except as otherwise required by law, all requirements or privileges relating to evidence or procedure shall apply equally to agencies and persons. Every agency is granted all authority necessary to comply with the requirements of this chapter through the issuance of rules or otherwise. No subsequent legislation shall be held to supersede or modify the provisions of this chapter or its applicability to any agency except to the extent that such legislation shall do so expressly.