Costumes from the TV show are eligible for Deployment up to a Tier 3. As are costumes from Comics.
As it states in the FAQ:
"In order to be deployed, a costume must be from an official Microsoft or 343i source. While this is primarily the games, Graphic Novels, Live Action Productions, Animated Projects, and even some concept art from Official published Art Books can be considered." (Emphasis added.)
In this case the question was whether items from a Fan made mod would be acceptable for a Tier 3 Deployment.
In order to qualify costumes must be from an official Microsoft, 343, or Bungie source. The live action show is considered a Microsoft and 343 product. A new type of helmet, backpack, or accessory added to a model and placed in a fan mod would not, because it is unofficial and made by a fan. So it might appear "in game" but it was added to the gane by a fan, not by the developer, and does not appear in the official product, and would not qualify for Tier 3.
In this specific case, the changes to the Marine backpack, color of their soft goods, and addition of a balaclava would be okay for a Tier 1 or possibly Tier 2 Deployment, but would not qualify for Tier 3 because they are not seen in the official, canon, version of the game.
