a. Nothing contained in this chapter shall be construed as authorizing the commission, in acting with respect to any historic district or improvement therein, or in adopting regulations in relation thereto, to regulate or limit the height and bulk of buildings, to regulate and determine the area of yards, courts and other open spaces, to regulate density of population or to regulate and restrict the locations of trades and industries or location of buildings designed for specific uses or to create districts for any such purpose.
b. Except as provided in subdivision a of this section, the commission may, in exercising or performing its powers, duties or functions under this chapter with respect to any improvement in a historic district or on a landmark site or containing an interior landmark, or any landscape feature of a scenic landmark, apply or impose, with respect to the construction, reconstruction, alteration, demolition or use of such improvement or landscape feature or the performance of minor work thereon, regulations, limitations, determinations or conditions which are more restrictive than those prescribed or made by or pursuant to other provisions of law applicable to such activities, work or use.