You don't necessarily need to execute a new note but you do need to modify it to add the due on demand clause.
This is a violation of the Reg. and subject to CMP if not corrected.
Sec. 215.11 Civil penalties.
Any member bank, or any officer, director, employee, agent, or other person participating in the conduct of the affairs of the bank, that violates any provision of this part (other than § 215.9) is subject to civil penalties as specified in section 29 of the Federal Reserve Act (12 U.S.C. 504).
I haven't looked at the CMPs for some time but if memory serves they can run from $5,000 up to $1,000,000 per day for each day the violation remains outstanding.
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The opinions expressed are mine and they are not to be taken as legal advice.