Section 30. A housing authority, with the written approval of the department and of the mayor of the city or selectmen of the town in which the project is situated, may enter into a contract with the federal government for purchasing or leasing a clearance or housing project owned or controlled by the federal government. If such a project has been so leased by a housing authority and such authority has by vote declared that the buildings of the project have been constructed in a manner that will afford necessary safety, sanitation and protection in other respects to the public, no changes shall be required by any agent of the commonwealth or of the city or town in the manner of construction, or the buildings, the fixtures or appurtenances thereto or the use for which the project was designed.