This is how I did it, although I still used windows for a small part (but mainly cos I'm paranoid).
First of all I'll just say that I found no way of finding out what type of VRAM you have in linux. Would love to know how to find out in linux, but I had to boot windows and run GPUZ to find out.
I used the following tools to mod/flash my bios:
atiflash - to save/load BIOSes.. apparently there is a linux version but I didn't really want to run an unknown binary on my linux box so I just used the windows version.
hexeditor/polarisbioseditor - You can use either of these to mod your bioses. PBE is written in c# so I see no reason why you couldn't get it running in linux. I used a hex editor.
Check sum fixer if you don't use PBT - I used the checksum fixer provided here
https://github.com/OhGodACompany . There are also tools here to overclock your cards and decode RAM timings.
I also found the strapmod.py tool handy (
https://github.com/nerdralph/strapread/blob/master/strapmod.py)
Good Luck!
