So not sure what you're trying to say here.
that flashing custom bios is possible
NOTHING CONCLUSIVE--
I tried reading the several threads that I found after searching earlier posts in this thread concerning user-modded 5700 series AMD graphics cards. The user claiming to be attempting BIOS mods and uploading them with ATIflash has poor English or is deliberately using LOLcat-speak. Nothing posted is legible enough to make sense.
Other long-time gurus explained that that the latest AMD cards have encrypted and signed BIOS. The Navi series won't accept a BIOS flash the way Polaris and earlier cards will.
If you can point me to a legible post or review explaining how to alter a Navi BIOS and flash it, please do. --scryptr
Still, AMD is releasing new bioses for the 5600, they raised frequencies and TDP allowance after Nvidia cut the RTX 2060 prices. This means the Navis can be BIOS flashed. Modified bioses is another issue.