No stipulation or agreement between the parties, their attorneys, or their representatives, with regard to any matter involved in any contested case before the agency, shall be enforced, unless it has been reduced to writing and signed by the parties or their authorized representatives, or unless it has been dictated into the record during the course of a hearing, or incorporated in any order bearing their written approval. This section does not limit a party's ability to waive or modify by stipulation or agreement any right or privilege afforded by these sections or by law, unless otherwise precluded by law.