The costs of surveying, selecting, and conveying lands granted to the Union Pacific Railroad Company shall become due and payable at and on the demand therefor made by the Secretary of the Interior as provided in , and nothing in sections 882 to 885 of this title shall be construed or taken in any wise to affect or impair the right of Congress at any time further to alter, amend, or repeal the Act of , chapter 216, as in the opinion of Congress, justice or the public welfare may require, or to impair or waive any right or remedy in the premises existing on , in favor of the United States. Sections 882 to 885 of this title shall be subject to alteration, amendment, or repeal.section 883 of this titleJuly 2, 18641864-07-02July 10, 18861886-07-10