Companies have been doing this for years. I flashed my Radeon 9800 to a 9800 Pro. It was the exact same hardware but the non-pro had lower voltages to prevent higher clocks. The X58 Asus P6T-SE I'm still running is the exact same board as the P6T, the only difference is that SLI is not supported by the BIOS so the board was cheaper as there was no licence to pay nvidia.
However you didn't pay 9800 pro money for the 9800, and not all of them supported that. Only second generation ones, when the wields were better and ATI didn't chop with laser the core, something NV does.
That period I had a 9700non pro, but made sure to buy a Club 3d with the ram in L positioning on the board. Because with a simple pencil I could make it run as 9700pro. A far more expensive card then back in Greece.