Truman Farm Home Expansion Act - Authorizes the Secretary of the Interior to acquire approximately five acres of land, including the structure located south of the Truman Farm Home site, as specified in the map "Harry S Truman National Historic Site Proposed Boundary" and dated April 17, 2003, for inclusion in the Harry S. Truman National Historic Site. Requires the Secretary to modify the boundary of the Site to reflect the acquisition of such land.