Regulations enacted by a board of county commissioners under sections 303.01 to 303.25, inclusive, of the Revised Code, shall not apply within municipal corporations, except that where county territory, subject to such regulations, is incorporated, such regulations shall apply therein and be enforced by the county officials until the election and qualification of the officers for the newly incorporated territory, and for not to exceed ninety days thereafter, to enable the officers of the newly incorporated territory to adopt zoning regulations. Upon annexation of county territory to an existing municipal corporation, the zoning regulations then in effect shall remain in full force and shall be enforced by county officials until the legislative authority of said municipal corporation shall either officially adopt the existing zoning regulations or new regulations for such territory.