No stipulation or agreement between the parties, their attorneys or representatives, with regard to any matter involved in any proceeding before the board shall be enforced unless it shall have been reduced to writing and signed by the parties or their authorized representatives, or unless it shall have been dictated into the record by them during the course of a hearing, 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 sections, unless precluded by law.