Version 0.5 is out.
Now you can select the skins for the start weapons.
You can select the DLC skins and can play with them until you cange the skin InGame.
Also you can select hidden skins like the employee and developer skins, but it seems that EPIC patched this way to get the skins. If its doesn't work for you just use the "Is EPIC employee" and "Is EPIC developer" boxes to get the skins. This has the advantage the game unlock you both skins and you can select them always InGame.
I hope the editor supports all skins now, because the many custom DLC packages confuse me :)