In the event that the State of Ohio shall levy, assess or impose any additional excise tax, or shall increase any excise tax presently payable by the Company during the period which this chapter shall be in force, then the rates fixed herein shall be so increased by the Company by filing a new schedule as to provide sufficient additional revenue to cover such new or additional tax or taxes. In the event that there shall be a decrease in any taxes levied, assessed or imposed against the Company by the State of Ohio during the period which this chapter shall be in force, then the rates fixed herein shall be so decreased by the Company by filing a new schedule so as to reflect the decrease. (1969 Code 53.09)