If anyone interested there is a bootable USB stick image with dual-boot (tinycore64 / ubuntu) where you can:
- Test your new / custom kernel
- Install, modify or change your setup without touching the eMMC
- Mount, repair, modify, or change your eMMC
- Test some other distro
It is a text based interface (Command-line), a full blow desktop interface can be installed if you have a fast USB stick with enough space.