Well technically all that would do is overclock your 7900 to 7950 speeds at a hardware level. Seems that is about all that is different between the two. You should see if your 7900 will run at 7950 clocks without a heat issue first. Then you can just use nibitor in the link above to create your own vbios with those speeds if you don't want to use something like rivatuner. Not sure why you would want to flash to 7950 vbios when you can just do the same thing with software (if your gpu can handle those speeds). You can also change the voltage to the gpu as well, but in a laptop with limited coolin you may be in for problems. What are you tryin to do exactly?
Then again maybe Isaac can help you there