To the extent permitted by applicable federal or state law, a plan of conversion may provide for a provision in the charter of the converted savings bank containing, in substance, the restriction set forth in RCW 32.32.230. There may also be included a restriction providing that the charter provision may be amended only by a vote of up to seventy-five percent of the votes eligible to be cast at a regular or special meeting of shareholders of the converted savings bank. If the converted savings bank elects to adopt the foregoing optional charter provision, the director shall impose, as a condition to approval of the conversion, a requirement that the converted savings bank fully enforce the charter provision.