Applicability. No person shall carry out any exterior modification, alteration, restoration, reconstruction, new construction, or moving of a landmark or property within a historic district; nor shall any person make any material change in the appearance of such property, its landscaping, signage, lighting, sidewalks, fences, paving or other exterior elements which affect the appearance and cohesiveness of the landmark or historic district, without first obtaining a certificate of appropriateness from the Historic Commission. However, this shall not be construed to prevent normal maintenance as provided for in § 300-55 of this article.