Modification of the terms of the power of attorney and subscriber's agreement of a domestic reciprocal shall be made jointly by the attorney and the board of directors. The modification shall be filed with the attorney and the department, and the filing shall by operation of law bind all subscribers the same as if each subscriber individually adopted and executed the modified, altered or amended subscriber's agreement and power of attorney. No modification shall be effective retroactively, nor shall it affect any insurance contract issued prior to the modification.