Every erasure, interlineation or alteration in any agreement with the crew (except additions made for the purpose of shipping substitutes or persons engaged subsequently to 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,-

(a) if in India, of some shipping master or customs collector; or

(b) if outside India, by an Indian consular officer or at any port outside India at which no Indian consular officer is available, any such person as is authorised in this behalf by the Central Government by notification in the Official Gazette.]