The way this bill is structured, it has two main parts: a charge and the output-based pricing system. Either part can be imposed on its own or they can be imposed together. The way that occurs is by adding the name of a jurisdiction to a schedule in the act by means of an order in council.
In your scenario where province X has a system that aligns with the national benchmark and then decides, no, it's scrapping that and eliminates it overnight, the federal government would then have the authority to issue an order in council. That would take some time, but could be done fairly quickly. It would then identify that jurisdiction on the schedule, and either one or both parts of the backstop would then apply in that jurisdiction.