The official of the state or any subdivision thereof who is charged with the duty of collecting any tax, interest and penalty, the collection of which is affected by the limitation hereinbefore provided, may, before the running of the five-year period of such limitation has been completed, enter into a written agreement with the taxpayer consenting to an extension of such period for an additional period of not to exceed two years, and any action or process may be brought or issued to collect such tax, interest and penalty at any time prior to the expiration of the period so agreed upon. The period so agreed upon may be extended for additional periods not in excess of two years each by subsequent agreements in writing made before the expiration of the period previously agreed upon.
The provisions of this section as hereby amended shall apply to tax periods ending on or after the first day of July, one thousand nine hundred seventy-eight, and the provisions of this section as in effect prior to the enactment hereof shall apply to tax periods ending before said date.