Section 16. (a) At any time after imposition of the surcharge, the legislative body may approve and the voters may accept an amendment to the amount and computation of the surcharge, or to the amount of exemption or exemptions, in the same manner and within the limitations set forth in this chapter, including reducing the surcharge to 1 per cent and committing additional municipal funds pursuant to subsection (b1/2) of section 3.
(b) At any time after the expiration of five years after the date on which sections 3 to 7, inclusive, have been accepted in a city or town, said sections may be revoked in the same manner as they were accepted by such city or town, but the surcharge imposed under section 3 shall remain in effect in any such city or town, with respect to unpaid taxes on past transactions and with respect to taxes due on future transactions, until all contractual obligations incurred by the city or town prior to such termination shall have been fully discharged.