This document adopts as a final rule, with some changes, proposed amendments to those provisions of the Customs Regulations that concern the issuance of administrative rulings and related written determinations and decisions on prospective and current transactions arising under the Customs and related laws. The regulatory changes involve primarily procedures regarding the modification or revocation of rulings on prospective transactions, internal advice decisions, protest review decisions, and treatment previously accorded by Customs to substantially identical transactions. The amendments are in response to statutory changes made to the administrative ruling process by section 623 of the Customs Modernization provisions of the North American Free Trade Agreement Implementation Act.