Nothing in this title shall be held to prevent any corporation, association or person mentioned in the first article of this title from granting transportation at the rate of one cent per mile to veterans mentioned in the preceding article, or their wives or widows; honorably discharged soldiers, sailors, marines and Red Cross nurses of the late world war to or from the annual convention, Department of Texas American Legion; any minister of religion for intrastate trips, or from granting to ministers of religion reduced rates of one-half the regular fare, or to prohibit the making of special rates for special occasions or under special conditions, provided authority therefor shall first be obtained from the Railroad Commission of Texas; or to prohibit transportation between points wholly within this State at the reduced rate of one cent per mile while traveling on official business connected with their respective offices, the following named peace officers, to wit: Adjutant General of this State; State rangers; the sheriff of any county, his deputies to be designated by him; constables; chiefs of police and assistant chiefs and captains; city marshals, chief of the detectives of any county or city, and assistant detectives.