N.Y.C. Admin. Code § 5-450: § 5-450 Agreements with owners.

a. It shall also be lawful for the board of estimate, with respect to a street closing, and the mayor, with respect to acquisition, either before of after the institution of a proceeding under this subchapter, to agree with the owners of the real property that will be affected by such closing, for and about the cession to the city of other real property included within the boundaries of any established street shown on the city map, in lieu of the real property comprised within the lines of the closed street, or to agree for and about the compensation to be made to such owners for the same or for and about the value of real property to be ceded in lieu of such discontinued or closed portion or portions of such street.

b. In case of any such agreement or agreements with part only of the owners entitled to and interested in the same real property so affected, for the purpose of making any such discontinuance or closing, or cession in lieu of such closing, the same shall be valid and binding upon the parties thereto, and the court shall nevertheless enter upon and make or proceed with its estimate, and tentative and final decrees as to the residue of such real property affected by the closing, concerning which the owners thereof shall not agree.

c. The final decree of the court shall be of like force and effect in regard to the matters comprised therein, as if no such agreement as to the part of the premises had been made.