Modification of federal adjusted gross income.

Whenever a person other than a corporation acquires, after the transitional date, as defined in sub. (13) (a) 6., a constant basis asset, the federal basis of which is different from the Wisconsin basis, an appropriate modification of federal adjusted gross income shall be made in the year of sale, exchange, abandonment or other disposition of such asset properly to reflect the income consequences of such difference. Whenever such a person acquires, after said transitional date, a changing basis asset the federal basis of which is different from the Wisconsin basis, appropriate modifications of federal adjusted gross income shall be made each year properly to reflect the income consequences of such difference; in any such case the secretary of revenue or his or her delegate may agree with the taxpayer for an amortization of such difference in basis over a period of 5 years or less.