How do we change our UN? Also is it a GA thing only?

You can change your username using an Identity Star Shuriken. This is available from the Cash Shop, shops, trades or Auctions.

You can change your UN by using an Identity Star Shuriken, which can be purchased through either the Cash Shop or user shops. I'm not sure whether you need to be a GA member at the time of using it, but I doubt it.

Thanks. (: