Any person employed in any of the offices to which these regulations
apply may be transferred without examination, after service of six
months consecutively since January 16, 1883, from one office to a
class no higher in another office, upon certification by the board of
examiners that he has passed an examination for the class in which he
is doing duty, and with the consent of the heads of the respective
offices and the approval of the Secretary of the Treasury.