This is guidance to federal agencies to update their policies to require free access for results they funded going forward. So, the issue is not to flip a swit

This is guidance to federal agencies to update their policies to require free access for results they funded going forward. So, the issue is not to flip a switch on a server to disable a paywall. The issue is to change official policy at many agencies, which will then trickle down. You can't just retroactively change the terms on existing grants.