If a taxpayer changes the tax year on the basis of which net income is computed, the taxpayer shall, at the time and in the manner the Department of Revenue prescribes, make a separate return of net income received during the period intervening between the end of the former income year of the taxpayer and the beginning of the new income year. [1957 c.632 § 6 (enacted in lieu of 316.520); 1987 c.293 § 58]