ASRock provides a warning on downgrading:
Due to BIOS code major upgrade to support Broadwell CPU feature, this BIOS update (P3.xx and after) will be backward compatible to Haswell CPU (E3 v3), but won’t be able to downgrade to P2.xx versions after upgrade to P3.xx BIOS.
For me the steps below worked and so far I have not experienced any issues in doing. But proceed at your own risk.
1) Create a FAT32 formatted USB DOS boot stick.
2) Get 2.00 Update BIOS Under DOS version from ASRockRack: http://asrock.pc.cdn.bitgravity.com/BIOS/Server/E3C226D2I(2.00)DOS.zip
3) Extract the ZIP File and copy the EXE file on the USB DOS boot stick. Then boot with it.
4) Start the DOS BIOS Updater with /X parameter: C:\226D2I~2 /x
Parameter /X ignores the current BIOS ROM ID
5) The updater will remain some time (approx 20 -30 secs) at 75%.
After this it will proceed. Just wait for some time to finish.
6) Restart and go into the BIOS. You will see it is downgraded to 2.00
7) Then use the BIOS Instant Flash feature to upgrade to 2.10. I UEFI patched version 2.10 before.
(if you compare above 2 pictures system time you will see it took approx 2 minutes, including booting and going into BIOS again 😛 )