Is it possible to do safely in BIOS so it runs on that as default?
This is what you should be doing: Figuring out your best hashrate, and then undervolting to save power and keep temps down. Undervolting will not affect your hashrate at all (unless you undervolt too low, and your GPU crashes. You'd know if that happened ).
Check out VBE7. It's a way to edit your GPU's BIOS with lower voltages, so it will always run at the new, lower voltages. We use this method because there's no way to undervolt in Linux, but it also works in Windows just as well, cuz it's done by the GPU BIOS, not any software that's running. I undervolted our GB 280x from 1.13 to 1.01V, and they run at <70C all the time.