@tomekmak You should be able to downgrade BIOS (including ME region) using Intel’s Flash Programming Tool (FPT):
I have written a guide on how to use FPT to downgrade the BIOS here.
Just remember that this motherboard has the Gigabyte DualBIOS feature which means that the backup BIOS chip likely has the more recent Kaby Lake BIOS (F20 or F21) with the updated ME firmware, so if your system fails to boot due to BIOS corruption for any reason - the backup may load without any warning and the system may not POST without clearing CMOS.
It is possible to flash the backup BIOS chip using EFIflash. I have posted a guide and download links for EFIFlash here.
Good luck!