The game doesn't support an addon interface, so the only addons that exist are made by hacking into the game's software, which is expressly against the ToS.

The reason why there isn't an officially supported interface (enabling addons without hacking) is in part because of SE's stance against damage meters, but I suspect that it's more to do with their concern for keeping the computer and console systems on an equal footing and the difficulties with getting an addon system to work on consoles. After all, if it was just about meters, they could provide an addon interface that didn't expose damage numbers to the addons.