BK got lucky with the bathtub and shower having the identical part.
If that had not been the case, I would have asked if the shutoff valve is in a reasonably accessible place, because if so, you could open it when you want to use the shower and then turn it off again. But it very likely isn't. I don't have the slightest idea where mine for the showers are. Only the ones for the toilets and sinks are accessible in the usual places.