Is there an option to change skins? For example if my brother got the forest skin with his pre order and would like to switch to default or any other skin he may have would he be able to? Or do all sets or armour come with 1 skin that cannot be changed?
The skins each are applied to a certain set of armor. The Forest skin is only applied to the HAZOP armor set. If you have the armor/skin code registered, that set of armor will immediately become available for wearing. This means that you do not have to rank up to acquire the armor. HOWEVER, if you do not like the armor with the skin, you will have to rank up until you acquire the original set.
This means that all the HAZOP armor pieces with the “Forest Skin”(immediately acquired) are…
Helmet=HAZOP FRST
Torso=HAZOP FRST
Shoulders=HAZOP FRST
Forearms=GV-09 Locking FRST
Legs=RG-63 Counter FRST
However, if you don’t like the skin, you will have to unlock these by ranking normally…
Helmet=HAZOP
Torso=HAZOP
Shoulders=HAZOP
Forearms=GV-09 Locking
Legs=RG-63 Counter
And in case you are wondering, you cannot currently put a certain skin on different armor. For example, you cannot put the “Forest Skin” on the “Soldier” armor set.(I really wish we could though)
I hope this helped 
-Cold Brass