Other than State law issues, TRID would be triggered either way if you take a lien on the dirt for the additional funds.
Having said that, we have, from time to time simply modified the original construction note and added overruns...quick and simple and friendly for the customer.
For this, I would make certain your State has no prohibitions on added money via modification.
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My opinion only. Not legal advice.
Say you'll haunt me - Stone Sour