HRS §490:2-202
When written agreements can't be changed by earlier talks
This section says that if a written agreement is meant to be the final word on certain terms, you can't use earlier agreements or side oral deals to contradict it. However, you can explain or add to it using trade practices, past dealings, or extra terms that don't conflict, unless the writing is meant to be the complete and exclusive agreement.
everyone
The statute, as written — Final expression: parol or extrinsic evidence
Terms with respect to which the confirmatory memoranda of the parties agree or that are otherwise set forth in a record intended by the parties as a final expression of their agreement with respect to such terms as are included therein may not be contradicted by evidence of any prior agreement or of a contemporaneous oral agreement but may be explained or supplemented by: (a) Course of performance, course of dealing, or usage of trade (section 490:1-303); and (b) Evidence of consistent additional terms unless the court finds the record to have been intended also as a complete and exclusive statement of the terms of the agreement.
Sections this one refers to
§490:1-303 How past actions and trade customs affect a contract
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