I don't think if you flash your Nvidia GPU with modded bios your hashrate doesn't change or no improvement this is just what I heard from other Nvidia miners that they already tested flashing Nvidia but it doesn't help to improve performance.
If you want to improve the mining performance of your nvidia card overclocking is enough and if you are mining ETH there is 3rd party software that works on GTX 1080 and 1080ti to improve performance they called it ETHenlargementPill. It works on my GTX 1080ti almost 45% increase in mining performance.
You can check this software from here
https://bitcointalk.org/index.php?topic=3370685.0