The people of the city, by their approval of this chapter at election, hereby authorize the city council, by ordinance duly enacted, to make such administrative and technical changes or additions in the method and manner of administrating and enforcing this chapter as may be necessary or proper for efficiency and fairness, except that the rate of the tax provided in this chapter shall not be changed without approval of the qualified electors of the city as provided by law. (1991 Code § 9-163)