Section 20. The proceeds of any sale of bonds or notes, except premiums and accrued interest, shall be used only for the purposes specified in the authorization of the loan, and may also be used for costs of preparing, issuing and marketing such bonds or notes, except as otherwise authorized by this section. If a balance remains after the completion of the project for which the loan was authorized, such balance may at any time be appropriated by a city, town or district for any purposes for which a loan may be incurred for an equal or longer period of time than that for which the original loan, including temporary debt, was issued. Any such balance not in excess of one thousand dollars may be appropriated for the payment of the principal of such loan. If a loan has been issued for a specified purpose but the project for which the loan was authorized has not been completed and no liability remains outstanding and unpaid on account thereof, a city by a two-thirds vote of all of the members of the city council, or a town or district, by a two-thirds vote of the voters present and voting thereon at an annual town or district meeting, may vote to abandon or discontinue the project and the unexpended proceeds of the loan may thereupon be appropriated for any purpose for which a loan may be authorized for an equal or longer period of time than that for which the original loan, including temporary debt, was issued. Any premium received upon such bonds or notes, less the cost of preparing, issuing and marketing them, and any accrued interest received upon the delivery of said bonds or notes shall be paid to the city, town or district treasury. Notwithstanding the provisions of this section, no appropriation from a loan or balance thereof shall be made which would increase the amount available from borrowed money for any purpose to an amount in excess of any limit imposed by general law or special act for such purpose. Effective with the fiscal year 2005 tax rate approval process, additions to the levy limit for a debt exclusion are restricted to the true interest cost incurred to finance the excluded project. Premiums received at the time of sale shall be offset against the stated interest cost in computing the debt exclusion. The provisions of the preceding 2 sentences shall not apply to bond premiums received on or before July 31, 2003.