Yes it is fixed! Inside the original firmware. You can change the voltage from 0600 to 0900 on my firmware.
The effect? I don't know atm. what are the differences.
I just did S7 Undervolt testing. The voltage must be fixed because there was no noticeable change if power consumption at the wall and I tried every voltage lower than the default voltage. I posted this on another thread here:
https://bitcointalk.org/index.php?topic=1512744.40
With my utility costs and the current difficulty level, my S7-B7 Miner is now breaking even with the halving reducing the block reward at 12.5 BTC. I was hoping this firmware was going to be able to undervolt the S7 and it was the reason I purchased the firmware.