Best way and recommended method are ASUS USB BFB, use small disks, fat32 and try different brands, test first with original CAP file. Some Asus boards are “picky” on this…
Intel FPT tool is another option, if the tool can access SPI regions for write operations,
unlocked FD.
EDIT: Yeah, my bad…AMD platform.
And yes, AMI MMTool will break CAP signature, for this remove CAP header by hex, later add it for complete valid CAP
For REBAR and related issues, please post here: [Release] Resizable BAR BIOS EFI Module - BIOS/UEFI Modding / BIOS modules (PCI ROM, EFI and others) - Win-Raid Forum