This section does not authorize the validation, ratification, or legalization of any violation of law or regulation in effect at the time of the action by the district council under this section. In accordance with its zoning laws, the district council may provide for the grant of power to the Board of Appeals of Prince George’s County on appeal to allow: an extension of a lawful nonconforming use throughout all or a part of a building in which the nonconforming use lawfully exists; the restoration or reconstruction of an existing lawful nonconforming use if by fire or other calamity the use has been destroyed to the extent of not more than 75% of the reconstruction value of the building in which the lawful nonconforming use was carried on; or an extension of an existing lawful nonconforming use on the same lot as the lot existed as a single lot under single ownership when enactment of the zoning law made the then existing use on the lot nonconforming.