A sub­sti­tute for any orig­i­nal propo­si­tion under debate or for any pend­ing amend­ment to such propo­si­tion may be enter­tained notwith­stand­ing that at such time, fur­ther amend­ment is admis­si­ble, and, if accept­ed by the Board by a vote, shall entire­ly super­sede such orig­i­nal propo­si­tion or amend­ment, as the case may be, and cut off all amend­ments apper­tain­ing thereto.