When any school district described in Section 32-5 has heretofore issued bonds or other evidences of indebtedness, on account of any public school building, or for any other purpose, which are now binding and subsisting obligations against such school district and remaining outstanding, such school district may, upon the surrender of any such bonds or any part thereof, or other evidences of indebtedness, issue in lieu thereof, to the holders of the bonds, or to any persons, for money with which to take them up, new bonds in accordance with the provisions of Sections 32-5 to 32-5.4, inclusive; provided, such bonds shall not be issued so as to increase the aggregate indebtedness of such school district to exceed, including existing indebtedness, 5% of the taxable property of such school district, to be ascertained by the last assessment for State and county taxes previous to incurring such indebtedness.