I’m pretty sure the law that created the U.S. Board of Geographic names gives it the authority to make that change and no congressional action is needed.
By golly, I think you’re right.
President Benjamin Harrison signed an Executive Order on September 4, 1890, establishing the United States Board on Geographic Names. The Board was given authority to resolve all unsettled questions concerning geographic names. Decisions of the Board were accepted as binding by all departments and agencies of the Federal Government.
https://en.wikipedia.org/wiki/United_States_Board_on_Geographic_Names