No problem. Here is the New York law on Accord and Satisfaction:
2010 New York Code
GOB - General Obligations
Article 15 - MODIFICATION AND DISCHARGE OF OBLIGATIONS
Title 5 - (15-501 - 15-503) ACCORD AND SATISFACTION
15-503 - Offer of accord followed by tender.
§ 15-503. Offer of accord followed by tender. 1. An offer in writing, signed by the offeror or by his agent, to accept a performance therein designated in satisfaction or discharge in whole or in part of any claim, cause of action
, obligation, or lease, or any mortgage or other security interest in personal or real property, followed by tender of such performance by the offeree or by his agent before revocation of the offer, shall not be denied effect as a defense or as the basis of an action or counterclaim by reason of the fact that such tender was not accepted by the offeror or by his agent.
So, what this means, "in plain English," is that if you write on the check that this is in full and final payment of a disputed debt, and the creditor cashes the check, then the matter is settled, unless the creditor reserves rights.
If the creditor cashes the check and reserves rights, then the creditor can still come after you for the remaining amount of the charge.
The way in which the creditor may preserve his rights is as follows:When a payment is received by check
with a notation on the front or the reverse side that the check is given in full payment, the creditor can deposit the check, if–and only if–the creditor preserves its right to pursue payment for the balance due. On the reverse side of the check below the customer’s notation, the creditor MUST
stamp, write or type in the following language: This check is deposited under protest, without prejudice, and with preservation of all rights of the payee against the drawer of this check pursuant to UCC § 1-207.
If the creditor does this, he has preserved his rights. If he has not written in this language, then you have an accord and satisfaction and the debt would be satisfied in full by the payment of the $100 with your notation that it was full and final settlement
Good luck with this. I wish you all the best.