The commission may by amendment of an existing franchise ordinance grant to the individual company or corporation operating a public utility thereunder the right to extend the appliances, fixtures and service of such utility in the streets, alleys, public ways, places and grounds of the city. Any such extension of a public utility shall become a part of the aggregate property thereof, shall be operated as such, and shall be subject to all the obligations and reserved rights in favor of the city contained in this charter and in the original franchise under which such utility is being operated. The right to use and maintain any such extension shall terminate with the original franchise and shall be terminable as provided in Section 107 of this charter.