I agree that the WSR require some interpretation to get to the right result. I think a simple solution is to replace "Only one ball may be called on each shot," by "If more than one ball is called on a shot, any pocketed ball will be treated as if it were uncalled." I see no reason to make calling two balls a foul -- it's just not a call.... Although the proper outcome under BCAPL rules would probably be similar if enforced under WSR, you have to do some tap dancing to get there under WSR. Calling more than one ball is not listed as a foul. And interestingly enough, WSR has no "otherwise violates the rules" provision specifying penalties for actions which may violate a rule but are not listed as a foul under WSR. Nor is there any other reference to a penalty for calling more than one ball under WSR 1.6, and the rest of 1.6 is fuzzy at best. ...
I notice now that 1.6 also needs: "The shooter may change the called ball prior to taking the shot.