Is there any way to link .kicad_mod files to the Footprint Viewer or start them from command line directly? Currently, it is just a window started by kicad.exe and no separate subprocess.
During footprint development it would be much easier to verify the footprint, if it is started right after generating them.
The footprint editor is not a separate binary. So it can not run on its own. (At least in v5. Not sure how this was in older versions.)
If you have the lib that holds your new footprint added to the library table then you can update the view of the footprint by reopening it from within the footprint editor. (In v5 and v4 simply press the open footprint button. The current footprint should already be pre selected so pressing ok will update it. In current nightly simply double click on the footprint in the library view.)
If you don’t have the footprint inside a lib that is part of your library setup then you can use the import button from within the footprint editor. (This is again simpler the second time around as the footprint editor will remember from where you imported the last footprint.)