In the case of bond trustees, who not only handle the money and funds of such county or district, but who also govern and administer the affairs of their respective county or district, including the issuance and sale of bonds and the building and construction and maintenance of the roads and bridges thereof, then the provisions of this chapter shall apply only to the interest and sinking funds thereof, and such bond trustees shall continue in office and in the performance of their duties in the administration of the affairs and business of such district as may be authorized by law.