In case of the division of existing land districts by the erection of new ones, or by a change of boundaries by the President, all business in such original districts shall be entertained and transacted without prejudice or change, until the offices in the new districts are duly opened by public announcement under the direction of the Secretary of the Interior. All sales or disposals of the public lands heretofore regularly made at any land office, after such lands have been made part of another district by any Act of Congress, or by any act of the President, are confirmed, provided the same are free from conflict with prior valid rights.