It's more complicated than that. Everything that calculates differences between two points in time for example would need to be updated to know about when the

It's more complicated than that. Everything that calculates differences between two points in time for example would need to be updated to know about when the switch occurred. And more generally, this is an example of why it's complicated - because it's easy to overlook things that could be affected, so there's a great deal of investigation and testing that would need to be done.