The problem with the capacitor fcstd files that one can get from our generators is that there is no information in the freecad file about how it is made. That part is all in the python script. Freecad only ever sees the final result. (The generators make an fcstd file, a step file and a wrl file but we only keep step and wrl)
This is however different for other models that are purpose made in freecad as found in this repo https://gitlab.com/kicad/libraries/kicad-packages3D-source So while this does not have stuff for elcos in it might be a good starting point for other components.
And you can search this old forum thread. 3D new library for Mechanical CAD exporting and enclosure design I remember that people posted CAD files in it that should be modifiable. But fair warning that thread is nearly 400 posts long so finding something in it might not be easy. And some of the files posted there are made in expensive software not in freecad.