481.1. Once only in each fiscal period, the council may by resolution order the rate of interest fixed by it pursuant to the third paragraph of section 481 applied also to the principal of taxes unpaid before the beginning of that fiscal period, for the duration of that period and every subsequent period for which the council does not fix a different rate by virtue of this section. However, it does not apply to the whole or any part of the principal of a tax paid between the beginning of the fiscal period and the date of passage of the resolution. The clerk shall give public notice of the passage of the resolution.