What do you mean by ‘a player that decodes an app on an AppleTV’?

If your AppleTV is running an app that is playing media, that app is the player. And that app will add the new keys, that it finds in the media it is playing, to its revocation list so that app can no longer play any protected media to the blocked device. It will refuse to communicate with the inline box because the key used by the box is now on the revocation list.

And there probably is some mechanism that causes this to apply systemwide, either because the encryption and list management is in some dedicated chip or because the list is shared systemwide.