Overwriting existing PYTHONPATH

I am attempting to install your software into a cluster in a GNU environment module, loading other modules for its dependencies. But this line breaks that modularity:
https://github.com/bcgsc/physlr/blob/4d32a9924df024b6e69937fb2d4cec781168e243/bin/physlr-make#L41

Must it overwrite `PYTHONPATH` instead of prepending?