Notwithstanding § 46.2-917, any person holding a special or charter party certificate issued by the State Corporation Commission or the Department pursuant to Chapter 23 (§ 46.2-2300 et seq.) of this title may transport special or charter parties in school buses provided all lettering required by § 46.2-1089 and warning devices required by § 46.2-1090 are covered with some opaque detachable material.