Any estate, interest, or lien held by the board of supervisors under the provisions of Section 17109, or under the provisions of Section 9 of an act entitled “An act to provide for the aid and relief of indigents,” approved June 5, 1933, may be subordinated by them to the lien of any mortgage or deed of trust given to renew or refinance any mortgage, deed of trust, or other encumbrance, the lien or charge of which had priority over such estate, interest or lien.