Section 13B. In a city or town which accepts the provisions of this section, the board of a county, city, town or district making the order for the assessment of any betterment, or balance of any assessment apportioned in accordance with the provisions of section thirteen, shall, upon the application of the owner of the real property assessed, if such owner is eligible for an exemption under clause Forty-first A of section five of chapter fifty-nine, enter into a deferral and recovery agreement with such owner on behalf of the city or town. In any instance in which a board of the commonwealth makes an order for the assessment of any betterments, said board of the commonwealth may enter into a deferral and recovery agreement on its own behalf in accordance with the terms of this section. Any such application shall be filed with the appropriate board within sixth months after notice of such assessment has been sent out by the collector. Such application may be filed with the clerk or secretary of said board, or delivered by mail or otherwise at their office.

The said agreement shall provide:

(1) that no sale or transfer of such real property may be consummated unless the betterment assessment which would otherwise have been collected on such real property has been paid, with interest as applied in accordance with the provisions of section thirteen;

(2) that upon the demise of the owner of such real property, the heirs-at-law, assignees or devisees shall have first priority to said real property by paying in full the total betterment assessment which would otherwise have been due, plus interest; provided, however, if such heir-at-law, assignee or devisee is a surviving spouse who enters into a betterment assessment deferral and recovery agreement under this section, payment of the betterment assessment and interest due shall not be required during the life of such surviving spouse;

(3) that if the betterment assessments due, plus interest, are not paid by the heir-at-law, assignee or devisee or if payment is not postponed during the life of a surviving spouse, such betterment assessments and interest shall be recovered from the estate of the owner; and

(4) that any joint owner or mortgagee holding a mortgage on such property has given written prior approval for such agreement, which written approval shall be made a part of such agreement.

In the case of each betterment assessment deferral and recovery agreement entered into between said board making the order for the assessment of a betterment and the owner or owners of such real property, said board shall forthwith cause to be recorded in the registry of deeds of the county or district in which the city or town is situated a statement of their action which shall constitute a lien upon the land covered by such agreement for such betterment assessment as has been assessed under the provisions of this chapter, plus interest as hereinafter provided. The statement shall name the owner or owners and shall include a description of the land. Unless such a statement is recorded the lien shall not be effective with respect to a bona fide purchaser or other transferee without actual knowledge of such lien. The filing fee for any statement recorded on behalf of a board of the commonwealth shall be paid by the owner or owners of such real property. The filing fee for other such statements shall be paid by the city or town and shall be added to and become a part of the taxes due.