It's a bit difficult to disentangle the libraries, at least at the moment. I would suggest to live with them and concentrate on the Lua code if you want to start to get your hands dirty with code. It's plain Lua, plus some interfaces for document handling (you don't need those for your plans) and some for input handling and graphics, like fonts, images and blitting them onto the screen. I suggest to read some of the Lua files, especially the file manager related ones, plus the main file. You can just edit them: Lua is a scripting language. For a quick start, I would just live with the executables as they are.
More or less this is the approach how librerator became its own software, derived from KPV.