For the purpose of promoting health, safety, morals, public convenience, general prosperity, and public welfare, the board of county commissioners of any county is hereby empowered to regulate and restrict within the county the subdivision of land. This chapter shall not serve to invalidate any ordinance, resolution, regulation, decision, plat approval, or other action taken or adopted, by a board of county commissioners or county planning commission, prior to or subsequent to July 1, 1981, which regulates or otherwise affects the subdivision of land, except that, subsequent to July 1, 1981, the provisions of section 11-33.2-12 shall apply to any county requiring plat approval as a prerequisite to the subdivision of land.