Hey! Sorry for the late response!
Unfortunately we can’t easily share the PSD files (since we can’t really attach them to the marketplace asset)
The user interface kit can be edited without it though. We are using textures which you can certainly replace with your own - and even export them through the UE4 editor so that you can create a base for your own designs. The only ‘downside’ (actually not a real downside - there’s just no other way) is that you have to follow the same way we used to “cut” the textures. For example you’ll have to create the slots, the separators and the left-right side of the actionbar the same way we did. You have to see the existing textures for that!