Such refunding revenue bonds may be exchanged on the basis of par for par for the securities to be refunded, or such bonds may be sold at not less than their par value and accrued interest and the proceeds received shall be used to pay the securities which are to be refunded thereby; provided, that in any case where the outstanding security holders are willing to accept any sum amounting to less than the total of the principal and accrued interest on any such outstanding securities such refunding bonds may be sold at a price which will cost the municipality not to exceed the maximum rate authorized by the Bond Authorization Act, as amended at the time of the making of the contract, computed to maturity according to the standard tables of bond values.
     With respect to instruments for the payment of money issued under this Section either before, on, or after the effective date of this amendatory Act of 1989, it is and always has been the intention of the General Assembly (i) that the Omnibus Bond Acts are and always have been supplementary grants of power to issue instruments in accordance with the Omnibus Bond Acts, regardless of any provision of this Act that may appear to be or to have been more restrictive than those Acts, (ii) that the provisions of this Section are not a limitation on the supplementary authority granted by the Omnibus Bond Acts, and (iii) that instruments issued under this Section within the supplementary authority granted by the Omnibus Bond Acts are not invalid because of any provision of this Act that may appear to be or to have been more restrictive than those Acts.