Technically it's not allowed.
So do DPS meters.
But you know they still work.
These are grey areas.
SE has no way to tell if someone uses either unless you post screenshots and videos with it.
Even then screenshots and videos are not hard proof for bans since according to SE they can be edited.
I really doubt they will do anything against modding though part of this because it requires too much effort to develop anti cheat methods for something that's purely cosmetic and visible only on your side.
Like I said keep low profile and don't ask/don't tell in game or in the official forums.
Or they can officially allow 3rd party plug ins like ESO does but I guess that's overly complicated due to policies and security.