Legal Question in Banking Law in Massachusetts

It will not be illegal, but it will not negate the language "For Settlement of All Claims." If you cash the check, it will be as if the language was not crossed out.

Basically you can treat the check as being contingent, ie... the payor is only going to give you the money if you accept that it is for full settlement of the debt. If you as the payee cash the check, it is accepting that language.

The check is an offer, to settle, and you accept it by cashing the check. There is nothing illegal about it, but it is a contract.