[With regard to any county which is required to operate on a countywide system of road administration as described in Section 19-2-3, this section shall read as follows:]
No existing law providing methods for the construction or maintenance of any public highway, bridges or culverts of the county shall be affected by Section 65-15-9; and it does not supersede or impair the obligation of any county to levy a sufficient legal ad valorem tax for the purpose of construction and maintenance of public highways, bridges or culverts, or a sufficient ad valorem tax to pay the interest or principal of any bonds heretofore or hereafter issued for the purpose of building bridges and constructing public roads. Nor does it supersede or impair any right to issue bonds for any purpose, and it shall not alter, amend or repeal any statute except insofar as such statutes are inconsistent herewith.