But I gave up, because finally I used SSH Droid app for remote access and LAN Drive app to manage pictures remotely via SMB - I only hope it will be stable enough to be useful, but if so - I will not need physical access to device anymore. I'm also not sure if visible buttons would not affect the way it operates.
Anyway - thank you for your entire support - without you I wouldn't manage to achieve that.
Firmware modification is probably possible, but if you will follow this topic, you will find even names of applications I have installed on my Zoom.me to manage it without stock app.
I'm using Nova Launcher to manage installed apps, SSH Droid for FTP/SSH access and LANDrive to map my Zoom.me as a network drive in windows PC. That allows me to modify content of my zoom.me from PC. If you need other kind of access - I'm sure that you will find an apps which will do it for you.
Meant flashing. So, do you have the MTK or Allwinner?
With one button it might be difficult to enter the update mode, but if opened you could possibly connect some pins to make boot to fail thus making it to boot such mode... IDK.
Other possibility is to make your wifi to connect to your own server instead of http://ota.zoom.me/ and let it "update" itself.
Their update zips are signed using test keys so you can make your own. (If recovery keys aren't changed when updated.) Or if you can enter the recovery mode then install it from sdcard.