Armor Games often does an Armatar contest (see this thread: Armorgames Armatar Contest Winter) in the Art, Music, and Writing section of the forums. The Armatar contests are seasonal and Armatars generate by the contests are seasonal as well.
In short, the Armatar you had was only available for a limited time. You can keep an armatar past it's season (time limit), but if you change it to something else when it is no longer available you cannot change it back.
