BraiinsOS allows you full control over your asics frequencies and voltages, fans can be set at fixed speeds or ignored and sensors can be disabled/ignored. This allows the greatest flexibility, and with care you can find the best efficiency per hash board, but you can also harm the miner if you go reckless with the voltage and speed settings.
No, these settings cannot be changed per chip, only per board. This is probably a hardware limitation.
As always, at a given fixed speed lower the voltage until you see the actual/current hash rates differ too much then go back up a notch on that voltage. If you change the speed, do this again, remember this has to be done per board, as every board is different.