No stipulation or agreement between the parties, their attorneys or representatives, with regard to any matter involved in any proceeding before the agency shall be enforced unless it shall have been reduced to writing and signed by the parties or their authorized representatives, or incorporated in an order bearing their written approval. This section does not limit a party's ability to waive, modify or stipulate any right or privilege afforded by these rules, unless precluded by law.
22 Tex. Admin. Code § 107.16