I don't know as I have not had to use it yet? But I think you are correct which is one drawback of the inflatable spare, since the entire wheel and tire must be replaced as a unit and since replacement tires are not available for the wheel. As I understand the doughnut Boxster 986 spare tire is replaceable. There must be a recommended mileage and speed limitation on the tire/wheel (not over 50 MPH as I recall)

It is a Vredestein tire. Vredestein

That is why I have a spare spare (986 Boxster spare).