In a contested case, no stipulation or agreement between parties, their attorneys, or representatives may be enforced unless it is reduced to writing and signed by the parties or their authorized representatives, or unless it is dictated into the record during the course of a hearing. This section shall not be interpreted as limiting a party's ability to waive, modify, or stipulate any right or privilege afforded by these sections, unless precluded by law.
28 Tex. Admin. Code § 1.31