Copy & paste from my post here.
The Python SDK offers a possiblity to automatically install Python packages through pip when installing using the requirements.txt. Some changes to the virtual environment of the tool might not be covered by this: For example, downloading and configuring language models for spaCy cannot be solved through the requirements.txt alone (similar for training corpora for NLTK).
So, as an idea for future versions of the SDK: Allow us to specify a Python script that is run when a tool is installed. This way we might be able to set up the environment, load additional tools etc.