I've created a mod that performs the changes I described above on the Kobo. If successful it should make Kobo <-> Win10 compatible without formatting/losing any files.
Take it with a grain of salt since I've only tested with my H2O, and only with a Win10 virtual machine, not a real Win10 PC.
Just because it works for me doesn't mean it will work for you. Use at your own risk.
Backup your files first.
To install, copy KoboRoot-fatpatch.tgz » .kobo/KoboRoot.tgz
[yes you have to do that on a PC that still sees the KOBOeReader drive, or with a Linux LiveCD - someone else will have to find/write a Windows program that does this directly in Win10]
After installing the mod, the reader will reboot, display a fat clown, and reboot again. At that point the mod performed the changes and removed itself (you have to reinstall the mod to re-try), and things should just work.
If you use this, please report back whether it worked or not.
Edit v2: Updated to have a longer delay before the operation starts, maybe that works better for older/slower devices
Edit v3: There was a bug that affected devices with 2GB storage which has FAT32 backup sector in a different place. Unbelievable.
Bug Notice:
This may cause power/screensaver settings to vanish after applying this mod. I'm not sure what's causing this yet. Workaround: rename the .kobo/Kobo/Kobo eReader.conf file to make Kobo return to default settings.
Edit v4: There was a syntax error that could cause the mod to get stuck and never reboot.
Experimental windows version here: https://www.mobileread.com/forums/sho...44#post3368644
~~~ Removed the fatpatch hack since Windows has released a patch that resolves this issue. ~~~