This subchapter and the Pennsylvania Avenue Development Corporation Act of 1972 (Public Law 92–578, 86 Stat. 1266) do not preclude other agencies or instrumentalities of the Federal Government or of the District of Columbia from exercising any lawful powers in the development area consistent with the development plan described in section 5(a) of the Act (86 Stat. 1269) or the provisions and purposes of this subchapter and the Act. However, the agency or instrumentality shall not release, modify, or depart from any feature or detail of the development plan without the prior approval of the Administrator of General Services.