How often would keys be rotated, and can that be done from the ground? And then, the nightmare of ensuring that updated certs for the keys get rolled out to all

How often would keys be rotated, and can that be done from the ground? And then, the nightmare of ensuring that updated certs for the keys get rolled out to all the devices so they don't all panic and say that the GPS isn't working at all anymore. For that, cell phones would probably be the easiest despite jerkass behaviour of manufacturers and service providers. Embedded GPS updating would be an absolute nightmare.