FYI:
I have mod/flash some setting into bios so I can automate the startup process. But I found it is very inconvenient because 1) everytime you want change the setting, you have to mod it again. 2) down time is too long if you have lots of GPUs on a rig and many rigs. command line argument (software way vs. hardware way) is far more easier and quicker.
If you're tweaking memory clocks / power settings, stick with Overdriventool. You can create a profile for each unique card, apply the appropriate overclock / undervolt settings, and then use the overdriventool command line + appropriate parameters to run in the same batch file as your Claymore startup file. This will apply the appropriate overclocks, and saves the headache of modifying the BIOS every time you have a simple change you want to test.