No, there's no way to downgrade to a previous bios version once you are running 2.2.1.  
I'm running Unraid on my system and after BIOS update (2.2.1) IOMMU has been disabled. This means that I'm no longer able to run VM on my second GPU. I know that IOMMU option was not visible in previous BIOS version but it was ON by default.I downloaded the older version of the BIOS (2.1.3) but it doesn't allow me to downgrade. Is it possible to do it with USB stick and BIOS_IMG.rcv?
Aurora R10, BIOS 2.2.1 disabled IOMMU, need downgrade