If subsequent to the recording of a mortgage on which all taxes, if any, accrued under this article have been paid, a supplemental instrument or mortgage is recorded for the purpose of correcting or perfecting any recorded mortgage, or pursuant to some provision or covenant therein, or an additional mortgage is recorded imposing the lien thereof upon property not originally covered by or not described in such recorded primary mortgage for the purpose of securing the principal indebtedness which is, or under any contingency may be, secured by such recorded primary mortgage, or an assignment of mortgage is recorded, such supplemental instrument or assignment of mortgage or mortgage shall not be subject to the tax or fee levied and imposed by Section 1904 of this title unless it creates or secures a new or further indebtedness or obligation other than the principal indebtedness or obligation secured by or which under any contingency may be secured by the recorded primary mortgage, in which case a tax is levied on such new or further indebtedness or obligation as heretofore provided in Section 1904 of this title, and shall be paid to the county treasurer before the time such instrument or additional mortgage is recorded. If, at the time of recording such instrument, or additional mortgage, any exemption is claimed under this section, there shall be filed with the county treasurer and preserved in the office of the county treasurer a statement under oath of the facts on which such claim for exemption is based. The determination of the county treasurer upon the question of exemption shall be reviewable on appeal to the district court under the same procedure as appeals from the county commissioners to the district court.