Thank you very much for your fast response. My (European) GX80 is in service right now, but I'll test your modifications ASAP.
I realize now that this will mostly push settings not meant for the camera to the camera, and it might or might not react to these settings. Not sure if battery saving mode of the G80 is a changeable setting over the html interface, but probably it won't work with the GX80. Max flash sync speed is not a setting, but rather a specification of the camera, so I guess it definitely can't be changed (unlike video bitrate, for which there might be a possible hack because of it also being a setting).
Have you already tried grabbing frames from the video stream that it also sends to these remote control apps? For example, you could create an "external recorder" for this. This would also, for example, allow higher ISO in video mode because you're really just grabbing the "raw jpgs" and creating a video out of it. Not sure how the bandwidth would hold up, you would need a good router and stable wifi connection, and even then the theoretical limit is around 300 Mbps, with the practical limit being much lower usually.