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