I don’t know of any guide to update the microcode in this forum, at least not something from me. I have less AMD knowledge on the matter and especially when it comes to AGESA replacements. That module is important and incorporates a lot more than cpu microcode so I suggest to not try replacing it with something from another board. Instead, you should replace just the cpu microcode, if possible. The easy way would be MMTool but it doesn’t seem to be able to detect or update AMD microcodes. So the only thing I can think of is manual cpu microcode replacement using UEFITool and copy-paste the new microcode data over the old one. I don’t know if that will work as AMD/AMI might have some other AGESA checksum or similar.
You haven’t mentioned what cpu microcode you want updated. I assumed you want cpu00600F20 (CPUID 600F20, FX-8350 etc) so I went with that. I updated it from 822 (03-01-2013) to 84F (25-01-2016) with UEFITool > Open ASUS CAP > Find the module where microcodes are stored by searching a random hex pattern of one mc extracted with MCE > Extract Body > Find 600F20 starting/ending point and replace the hex code within for the new mc (both are 0xA20 sized) > Replace Body > Save/Rebuild final image. UEFITool fixes automatically the BIOS volume checksum where the change is situated but as I said, if there is anything else from AMD or AMI at Agesa or similar, then the BIOS might not work. The mod is based on Crosshair V Formula-Z BIOS 2201.
Also, after the mod, the AMI Capsule (.CAP) might be invalid and thus the in-BIOS update might not allow you to continue. This excellent thread by Fernando might help in such a case.
Bottom line: This might or might not work. So, keep that in mind in case you decide to proceed and test the modded SPI image attached below. Either way, please keep us informed.
By the way, Windows can update the mc as well during OS boot via the mcupdate_GenuineIntel.dll and mcupdate_AuthenticAMD.dll libraries.
CROSSHAIR-V-FORMULA-Z-ASUS-2201_new.rar (3.18 MB)