Steps to create service tool with unity api

Hi, guys
I need to create tool that do some repacking of unity assets.
I took a glance at unity doc and found methods I need.
What docs should I dive into for make little exe-file that exploits these methods.
It’s preferable to use c++ or python (I can include unity headers, don’t I),
but unity is documented for js and some other languages.
So it can be js after all.
What steps should I do if I need one exe file implementing one task?

Unity assets are always created from the editor. Rather than writing python to mess about with Unity assets, just changed them in the editor and re-export them as AssetBundles. (Requires Pro.)