Preexisting nonconforming accessory signs may not be changed, extended or altered unless the change brings the sign into conformity with the provisions of this chapter or unless said change is limited to changing the sign letters or symbols and/or changing panels and does not alter the structure of the sign itself. The following preexisting nonconforming signs, however, may be changed, extended or altered if there is a finding by the Zoning Board of Appeals that such change, extension or alteration will not be substantially more detrimental than the existing nonconforming sign to the neighborhood, and provided that such change, extension or alteration will not make the sign any more nonconforming than it now is (i.e., higher, taller, bigger, closer, etc.):
A. Preexisting nonconforming accessory signs in residential districts.
B. Preexisting nonconforming projecting signs in the Central Business District.