Payments to be made as herein provided shall be in addition to, but not in duplication of, any payments that may otherwise be authorized by law. The means employed to acquire the property, whether by condemnation or otherwise, shall not affect eligibility for reimbursement or compensation under sections 277d–17 to 277d–25 of this title. Nothing contained in such sections shall be construed as creating any legal right or cause of action against the United States or as precluding the exercise by the Government of the right of eminent domain or any other right or power that it may have under such sections or any other law; nor shall such sections be construed as precluding an owner or tenant from asserting any rights he may have under other laws or the Constitution of the United States.