Changed the DDF using deCONZ (VNC), SSH to HA, login to deCONZ docker container, did a cp /usr/share/deCONZ/devices/blitzwolf/bw_shp13_smart_plug.json /data/.local/share/dresden-elektronik/deCONZ/devices/bw_shp13_smart_plug_MyCustomConfig.json.
Could not restart deCONZ yet (because of… productive reasons) to test if that storage is really persistent and the DDF stored in that location really overrides the default storage one.
One last question for now is related to the DDF content. I posted it in this other topic even it is a generic one, independently of specific devices. If that path line thing is sorted out I’ll try to restart the deCONZ Home Assistant addon asap and turn back with the results.