Guild Wars 2

It indicates that these are one time use only, I think that for 500 gems they should become purchasable from your Hall of Monuments vendor.

I believe that you can use the gem store armor skins more than once. As I understand it, for your 500 gems you are getting the skin and one transmutation for it, but after that you can just use transmutation stones to keep transmuting the appearance onto additional armor sets later. I pretty much think of them as armor skins that come with one set of “built in” transmutation stones.

It’s be nice if you could just transmute the skins onto armor as much as you like without any extra cost like the HoM skins, but IMHO having a unique skin with what is essentially unlimited transmutation stones to use with it would be too much to expect for 500 gems.