This act establishes a National Heritage Area System. The Department of the Interior may provide technical and financial assistance to local coordinating entities to support the establishment, development, and continuity of such areas. The National Heritage Area System shall be composed of each National Heritage Area, National Heritage Corridor, National Heritage Canalway, Cultural Heritage Corridor, National Heritage Route, and National Heritage Partnership designated by Congress before or on enactment of this act; and each National Heritage Area designated by Congress after enactment of this act. A National Heritage Area shall not be considered to be a unit of the National Park System nor subject to the authorities applicable to such units. Interior may carry out or review a study to assess the suitability and feasibility of each proposed heritage area for designation as a National Heritage Area. Interior must review and certify whether the proposed area meets specified requirements, including that it has natural, historic, and cultural resources that represent distinctive aspects of the heritage of the United States. An area shall be designated as a National Heritage Area only by an act of Congress. Interior shall conduct studies to assess the suitability and feasibility of designating specified areas in Hawaii as the Kaena Point National Heritage Area and in Virginia and North Carolina as the Great Dismal Swamp National Heritage Area. The act also (1) establishes or extends specified National Heritage Areas, (2) redesignates the America's Agricultural Heritage Partnership in Iowa as the Silos & Smokestacks National Heritage Area, and (3) extends the deadline for the management plans for certain heritage areas.