The provisions of Section 53531 shall apply only to coupon rates and shall not affect the power of a local agency to sell bonds at a discount below par if permitted by law. Any provision of law permitting bonds to be sold at a discount but specifying a maximum interest yield on bonds sold at a discount to the contrary notwithstanding, the bonds may be sold at a price yielding to the purchaser an effective interest rate of not to exceed 12 percent per year, payable as permitted by law, according to standard tables of bond values.