BIOS mods on Nvidia cards aren't difficult. Google 'NiBiTor' or 'Fermi BIOS Editor' and take a look at the utility.
Fermi BIOS Editor isn't being developed anymore, but it works fine on my 470/680 Fermi cards. For older non-Fermi cards, NiBiTor works fine for changes in the core clock, shaders and memory clock.
Just make a backup of the original file so you can flash back to it.