122.—Every erasure, interlineation, or alteration in any agreement with the crew (except additions made for the purpose of shipping substitutes or persons engaged after the first departure of the ship) shall be wholly inoperative, unless proved to have been made with the consent of all the persons interested in the erasure, interlineation, or alteration, by the written attestation (if in Her Majesty’s dominions) of some superintendent, justice, officer of customs, or other public functionary, or elsewhere, of a British consular officer, or where there is no such officer, of two respectable British merchants.