Hi! Yes, you can absolutely use the kit to create and commercially sell your own game. You can modify the mechanics, code, systems, assets, and other parts of the kit as needed for your project, including fixing or replacing systems.
The main restriction is that you cannot resell or redistribute the Horror Game Development Kit itself, or its assets/source files as a standalone product or asset pack. The finished game you create with the kit can be sold commercially.
I apologize for not including the license documentation with the pack originally. I’ve now prepared the license and will add it to the package so the terms are clear. Thank you for pointing this out!