It is possible, I have set of sapphire rx 470 4GB which I bought about month ago and they have different bios compared to the ones I bought a one or so earlier. The difference was with memory straps set at different location in the bios.
First time I head about it. Every time I wanted to flash bios on two cards with same memory (and same model of course) it worked just fine without creating bios for every single card independently