This tutorial is pretty good as an introduction to modding APKs:
https://old.reddit.com/r/ApksApps/comments/oat3qu/tutorial_how_to_modify_apk_files_for_premium/
The example used is unlocking premium features but the principles are the same for disabling DRM.
Sounds like Bython is the language for you! (only half-joking)
Since Whatbox allows you to SSH into your seedbox, you can setup slskd manually (root not required) and access its WebUI remotely.