I am not sure if I understood it correctly, but I will try to offer some guidance nonetheless!
-
As for the GUI assets both here in this pack and the Dragon Regalia: Yes, you can modify them as you see fit!
-
As for the PSD files: I can’t handle you PSD files because I don’t use photoshop for making these assets! Instead I work with aseprite. I could provide the .ase for a few of those, but I believe it will be of little to no help. Most of the .ase are, pretty much, the same files you will get on the packs as a .png, save a couple of them that are broken down into layers. For the GUI, almost all of them are single layer files;
-
The best approach here might be getting the .png themselves and just editing them to match your current system. The way I broke down the assets - such as the 9 slices - are supposed to be of more generic use, not aiming any particular system, so it is on the person using to edit or use them as they see fit;
Does this help in any way? Feel free to drop me any further questions or even suggestions for future GUI packages!