Modernizing Retrospective Regulatory Review Act This bill requires the Office of Information and Regulatory Affairs (OIRA) to issue guidance for using technology to retrospectively review existing federal regulations and, in consultation with relevant agencies, report on the progress of the federal government in making agency regulations available in a machine-readable format. Specifically, the OIRA report must (1) assess whether regulations of agencies have been made available to the public in a machine-readable format, and (2) provide information about the recognition by the Administrative Committee of the Federal Register of the Electronic Code of Federal Regulations (eCFR) as an official legal edition of the Code of Federal Regulations. Currently, the content of the eCFR is authoritative but unofficial. Additionally, not later than 18 months after the enactment of this bill, the OIRA must issue guidance about how a federal agency can use technology to retrospectively review the agency's existing regulations. Each agency must plan and implement a strategy to comply with the OIRA's guidance for the retrospective review.