The legal nonconforming use of any land and/or structure that existed at the time of adoption of the ordinance codified in this title may be continued, although such use does not conform with the provisions hereof; provided, no structural alterations, except as may be required or authorized by law or ordinance, are made hereafter. A nonconforming use may be changed to another nonconforming use of the same or more restricted classification as determined by the Code Enforcement Director of the City of Topeka or the Shawnee County Zoning Administrator, as applicable. A change in the district map shall not affect the status of a nonconforming use except in such case when the change brings the use into conformity. Whenever a nonconforming use has been changed or converted to a more restricted use or to a conforming use, such use shall not thereafter be changed or converted to a less restricted use. (Code 1995 § 48-28.01.)