Customizing the Jupyter launcher: How do I build the launcher package?

Dear all,
I would like to deploy an instance of Jupyter Lite. However, I want to modify the Launcher to be more a “start page” / “homepage” where the system is explained. Therefore, I would like to replace the Launcher content with my own (static) content. From the Github code, it looks like I need to patch jupyterlab/packages/launcher/src/widget.tsx. If I understand it correctly, this will then also patch the Jupyter Lite site that I generate. If I typically install jupyterlab, then I get the compiled version. How do I get in a conda environment jupyterlab built from the source such that I can modify the above file?

Sorry, if this is a trivial question, I am just new to Jupyter and a little confused how the package actually works compared to “regular” packages that are distributed via pip. I would very much appreciate if you could give me a hint how to get started using a fresh conda environment.