Any city or town which adopted the model city tax code may elect to amend the effective date of any provision of such code, or amend the effective date for application to any specified class of taxpayers of any provision of such code, to any date after the effective date of the original adoption of the code in any case where the city or town believes a substantial number of taxpayers may not have received a fair notice as to the applicability of such tax, or in any case where the city or town determines that a prospective application of a provision may further substantial justice. Nothing in this section is intended to require any city or town to take action.