The source code you see at GitHub can be loaded by Android Studio and you can modify, then compile it.
If you only modify a .kcm file then you will see its original name but when you use it, it will be your own layout, but the original name also can be modified in an .xml file.
Basically the .apk file is a compressed image (.zip), so theoretically you can modify its internals - you may open an existing .kcm then you can modify it, but I don't know if Android will accept this modified file.
You can not just drop the file into the filesystem unless you have root access, but another f