After the hearing of any objections to any change made or to the failure to make any change to which any taxable person considers himself entitled, and the making of any changes that may be deemed proper, the valuation as so ascertained shall, unless changed in the manner herein provided or as provided by existing law, stand as the valuation for the assessments for county and institution district taxes and for such other political subdivisions as levy their taxes on county assessments and valuations, in such county, until the next triennial assessment: Provided, That all taxes levied for the year one thousand nine hundred and forty-two, or any fiscal year commencing during the year one thousand nine hundred and forty-two, shall be levied and assessed on assessments and valuations made as heretofore provided by law.