No, it is not legally binding. One party may not unilaterally change the amount owed or terms of payment by doing this. There is a common myth that the memo line on a check has legal force - it doesn't. It's just for informational purposes. While it helps to identify the purpose of a check, it does not bind the recipient. Think about it, if it was that easy to alter the terms of a payment, everyone would do it. For example, a person could write "payment in full" for a bill and be done with it. Additionally, the fact is that not every check can be that closely monitored for such notations; it would tie up commerce. Bottom line, a recipient of a check without being bound by whatever may have been written in on the memo line.Answer: The notation in the "memo" line is not legally binding. You can negoatiate the check without any negative recourse.