I have tried modding the bios of various gpu's for my eth rigs, but every time I do it doesn't work right. So, now I am ready just to pay someone to do it for me. I want to lower the power consumption and raise the hashing power. Shoot me a pm with prices.
Can you give us more info about your ETH mining rig? I am building one myself with RX 470 and I have tried to mod it and successfully I'm getting a higher hash rate 24Mh/s comparing to 19-20MH/s.
Remember that some type of GPUs is better to not mod them because can't be as efficient as some other models can be so be careful. I'm sending you a PM requesting more details.