It doesn't apply to all cards, but have a look here (http://www.rojakpot.com/default.aspx?location=3&var1=92&var2=0) as it might get you those last few critical fps from the latest game you are running.
TL.
Is it true that if you try to mod a 9800 Pro that can't be turned into a 9800XT, it ruins the card?
I recall that being the case with the old 9800AIW > 9800 Pro mod, or something like that :)
In this case it is largely just a BIOS flash, so I guess you coudl say yes - if you bork the BIOS flash then you coudl be up the creek without a paddle in exactly the same way as you might be every time you try to flash your motherboard's BIOS. Most gfx BIOS are similar enough to run on other cards, but not perfectly so. Most mis-flashes are recovered by a reflash, but it is never guaranteed to work.
TL.