Hi, thanks for the interest.
It is possible to create new races or modify the existing ones.
If you open the chargen.pak file (it is a zip file) you can see how everything is defined in json files, and all the used textures.
Also, if you create a "data" folder in the app folder, and unzip the contents of the pak file to this folder, the app uses the lose files instead of the single archive.
This way anyone can try to add/modify things in the app.
I never wrote a guide detailing the process of creating a new race, but, for now, by checking the existing ones, and some patience, you can modify almost everything in the characters.
I haven't published the code to github yet. In the past the code was a bit messy and I wanted to clean it first. After I did clean it, I started building on it, trying to build a working game prototype. I think it now needs to be simplified a lot. Otherwise it would be a game engine (a simple game engine) and a demo application.
Time will tell.