The undertakers shall not erect any lighthouse or beacon, or exhibit or allow to be exhibited any light, beacon, or sea-mark, without the sanction in writing of the said Corporation of Trinity House, of the said Corporation for preserving and improving the Port of Dublin, or of the said Commissioners of Northern Lights, respectively, according as the harbour, dock, or pier is situated in England, Ireland, or Scotland, first having been obtained in that behalf; and if any such light, beacon, or sea-mark be exhibited with such sanction as aforesaid, the same shall not be afterwards altered without the like sanction; and every such light, beacon, and sea-mark shall be of such power and description, and shall be from time to time discontinued or altered, as the said Corporation or Commissioners respectively shall from time to time direct.