In all cases where a privilege tax is required for carrying on any business in this state, and a privilege license has been obtained for the same, and afterwards during the period covered by said license, the licensee shall desire to increase his business to a classification for which a higher privilege tax is required, he shall before increasing same, procure an additional license, but shall only be required to pay for such additional privilege license on such higher classification; the same to be prorated on the annual rate according to the number of months unexpired remaining in the period for which the original license was issued, and the additional license shall expire at the same time as the original license. The officer issuing the license shall certify on the face thereof that it is an additional license, and the period for which it is issued.