I have read that the bios is encrypted like verifyed and signed by amd, so no bios mod 
yupp, word is they actually added a little ARM CPU right on it to hard-secure the bios
You CAN flash it, but you get black screen on boot (as it checks for signed bios and black screens if not)
But fear not! there is hope yet! Our friendly(?) neighborhood Wolf0 is working on bypassing this!
see: http://www.overclock.net/t/1634018/vega-frontier-rx-vega-owners-info-thread/70#post_26281235 for details
I dont think they have gotten it QUITE open yet, but much progress has been made, i can see modding inna few weeks (hopefully)