We already know that the Skull Trooper is making a return to the Fortnite Item Shop with the new Skull Ranger, but it looks like there will be unlockable styles for both skins. Players that own the skin will be able to unlock the different style by completing specific challenges. The unlockable styles can be seen below, thanks to @TwoEpicBuddies:
The Ghost Portal Back Bling will also be available by completing challenges. This Back Bling was found in the files in previous patches and can be seen below:
You can read more about the Skull Squad Gear by clicking on the image below: