Mass. Gen. Laws ch. 183 § 22
A co-operative bank mortgage following in substance the form entitled "Co-operative Bank Mortgage" shall when duly executed have the force and effect of a mortgage deed to the use of the mortgagee and its successors and assigns, with mortgage covenants and upon the statutory co-operative bank mortgage condition and with the statutory co-operative bank power of sale, as defined in the two following sections, to secure the payment of the money or the performance of any obligation therein specified. If any buildings on the mortgaged premises shall be wholly or partly destroyed by a fire in respect to which the company or companies insuring the same shall deny liability to the insured, the mortgagee may at its option forfeit said shares, and, after applying the withdrawal value thereof to the payment of said loan, interest and fines, may assign the mortgage with the note and debt thereby secured to such company or companies upon payment by it or them of the balance then owing to the mortgagee on account of said loan; whereupon said note and mortgage shall forthwith become a note and mortgage payable on demand with interest at the rate set forth in said mortgage, payable semi-annually, the first payment of such interest to become due six months after the date of such assignment.
The parties may insert in such co-operative bank mortgage any lawful agreement or condition.
Mass. Gen. Laws ch. 183, § 22