They’d be doing this change on their TVs, in principle this would be no different from displaying the settings menu that comes up when you press the * button, no tampering of the HDMI signal required. HDMI inputs are their own “channels” in the UI so it’s pretty trivial to put ads on the screen periodically when one such channel is open.
six lobe and it’s variants are instruments of the devil, I swear I can’t ever get the screw size right for the life of me and get so paranoid about stripping screws.