I have 470D4U that may be bricked through a bad firmware update (BIOS / BMC). As sure the still seems to work but cannot access GUI, and can only control through impitool, additionally serial doesn’t seem to be working (Tried through port and SOL). My question is can i use IMPI commands raw or otherwise to forcefully downgrade the BMC firmware, enabling the GUI again?
Presumably you’ve broken the BMC but not the BIOS? otherwise the host system wouldn’t boot.
If you’ve got physical access to the system you’ll probably want to just reflash the entire BMC.
Grab the latest (or desired older) BMC .ima from the support page then follow the " How to update the BMC FW locally in DOS?" instructions on this page https://www.asrockrack.com/support/faq.asp#BMC
I’ve done this in the past to resolve the BMC’s gui breaking from a bad TLS cert installation.
Thank you, unfortunately I think the bios is also corrupted. It wont boot so I cannot get to a shell at all.
Ah I see. Fortunately the BIOS rom is socketed, you could either contact ASrock support to get a replacement rom chip, or get a programmer for the chip and reflash it yourself. I’m not super familiar with reflashing “raw” bios eeproms, but I think you only want to reflash a particular region of the eeprom which holds the bios image. The eeprom also holds board specific information (IDs, mac addresses maybe?) so you don’t want to reflash the entire thing.
Probably best to get asrock support to send you a new rom chip 
You might be able to reflash the bios from ipmitool using ipmitool hpm or ipmitool fwum, this seems to be used in documentation from IBM and Oracle, but I can’t find much detail on it. I think the firmware/bios image has to be prepared in a special format for these to work, and probably requires some level of hardware support. I don’t think you get either of those things on this board.