Mikoto doesn't block the update, just removes the badge in settings. Strange that your router hasn't blocked it?? I assume you've put the correct address in to block?
Quote,
Here are some known ways to prevent the auto-pushed update from being auto-pushed to your iOS device:
1. In your Wi-Fi router's settings, set up a block (using Access Restrictions or similar in the router's web interface) to mesu.apple.com. This will prevent your device from "phoning home" to Apple, checking for the update and getting the download auto-pushed to it again (it may repeatedly get auto-pushed again to the device, even if you remove the iOS update file from the device; see section 3 below). Note that your router may not have this ability to block access to certain locations. In this case, see #2 below. Also note that connecting to a Wi-Fi router other than your own (with this block in place) will expose the device to the auto-pushed update. The block will only be valid when using your own Wi-Fi network.
[doublepost=1489081292][/doublepost]Or install the NOOTA.mobileconfig for TvOS