Adding custom packages to Jupyter Lab?

Is there a way of making custom Python packages generally available within Jupyter lab?

While their documentation suggests to make install-able versions, and going through PIP, this is rather inconvenient for exploratory data science (especially, while I keep extending/developing these packages).

Usually I would point to the location of packages as a PYTHONPATH in .bash_profile (MacOS) – a step that would make them accessible in other contexts (e.g.: Jupyter notebooks) - but does not work with Jupyter lab (on the same machine).