N.Y. Comp. Codes R. & Regs. tit. 9 § 1640-1.4
Mandatory procedures are indicated by the word shall. Efforts have been made to limit mandatory procedures to those necessary to insure adequate control, or for the proper and uniform maintenance of accounts, or for the preparation of reports and financial data on a uniformly consistent and comparable basis, or to assure evidence of compliance with statutory requirements and the regulations of the Division of Housing. With respect to non-mandatory procedures, local agencies may adopt alternate methods to those recommended or described in this Subchapter provided the information requested or required is furnished in essentially the same form. However, the cost of performing any specific operation under a method other than that proposed in this Subchapter shall not exceed the cost of operation under the recommended plan.
N.Y. Comp. Codes R. & Regs. Tit. 9 § 1640-1.4