in Cinema 4D R20 the environment variable C4D_PLUGINS_DIR has been removed.
It has been replaced with g_additionalModulePath. You can use this command also as a command line argument.
See Environment Variables.
Please notice that you can mark your post also as a question. See Q&A New Functionality.
Set Driven Keys is just some workflow to create an Xpresso setup connecting two parameters. This has nothing to do with scripting or CallCommand().
Can you maybe explain somehow differently what you want to achieve?
Hi! You could go for CTracks via Python. You'd have to get the track for a position parameter, for example, or create one, then get curve, then add keys. Later, you could simply range map it back to your Xpresso rig. it It's definitely doable!