The original plan required a laser link, but those were removed from the v1 satellite because the lasers would survive reentry and SpaceX didn't want their satellites falling on anybody's head. So this is definitely a hardware upgrade requiring new satellites.
But that's not a big stumbling block -- SpaceX plans on replacing 1/5th of their constellation every year.
But that's not a big stumbling block -- SpaceX plans on replacing 1/5th of their constellation every year.