The office of county auditor may be combined with the office of county clerk in each county with a population of less than five thousand by unanimous resolution of the county legislative authority passed thirty days or more prior to the first day of filing for the primary election for county offices. The salary of such office of county clerk combined with the office of county auditor, and the salary of the office of county auditor that is not combined with the office of county clerk, shall be not less than ten thousand three hundred dollars. The county legislative authority of such county is authorized to increase or decrease the salary of such office: PROVIDED, That the legislative authority of the county shall not reduce the salary of any official below the amount which such official was receiving on January 1, 1973.