Taking over their DNS isn't going to help if they did things correctly. If they did things right each device is going to be doing cert verification with AWS IOT, and that verification will fail. That's client and server cert validation, unless they turned that off. On reset it should still verify the server cert when it tries to call home, but since you have access to the image you can replace that (if they didn't st…
If you had read the post, you would have seen that they did, in fact, not “do things correctly”.