That was before the era of VBIOS-signing. You straight-up can't boot any VBIOS image that's not signed anymore.
It was also before the era when PROM fuses were used to permanently disable hardware at the factory. So like, nowadays when you do something like flash Vega 56 with Vega 64 firmware, or flash 5700 with 5700XT firmware, it doesn't actually turn on any cores anymore, they're permanently disabled now. What changes is things like memory speed (Vega) or power limits (5700) that are used to artificially gimp the cards and increase the performance difference beyond the actual core count, as just disabling cores often doesn't give enough difference anymore to be marketable (Vega especially was very bottlenecked by other parts of the card other than the cores).
