I once saw a Boeing 727 that had been retrofitted with winglets. That was allowed, but Boeing no longer guaranteed the wings. So yes, it works just as you des

I once saw a Boeing 727 that had been retrofitted with winglets. That was allowed, but Boeing no longer guaranteed the wings. So yes, it works just as you describe. (Planes, not trains, I know, but it's still a datapoint on how liability works out there.)