Repairs, alterations, and improvements. Nothing in this article shall prohibit the repair, reinforcement, alteration, improvement, or modernizing of a lawful nonconforming sign or outdoor advertising structure, provided that such repair, reinforcement, alteration, improvement, and modernizing do not exceed an aggregate cost of 30% of the appraised replacement cost thereof, as determined by the Director of Community Planning and Development, unless the subject sign or outdoor advertising structure is changed by such repair, reinforcement, alteration, improvement, or modernizing to a conforming structure.