I would have to review all the documentation regarding this, however, it sounds as if it would be contrary to law and therefore unenforceable. You can not charge rent to a mortgagor because he is the owner of the land. What you are describing would be on the order of a strict foreclosure where if the mortgagor failed to pay you would automatically repossess the property and strict foreclosures are forbidden under NY law. You could charge late fees and have default provisions which would increase the interest rate as a penalty but rent would not be applicable. You need to have an attorney evaluate your documents and probably commence a foreclosure action.
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The mortgage instruments will recite what your remedies are for late payments. You cannot impose additional ones unless they are statutorily provided despite the language.
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