I try this on my S9 13.5Th, by flashing on interface web.
Freq and asicboost work perfect ! but not voltage

...
I set 700mhz and 900mv and apply , the miner boot correctly at 700mhz but 870mv ...
Hi, the voltage and freq is being set from outside bmminer on this version because of the closed source code which was not released yet, you are not going to see in the logs of bmminer saying the voltage. You will see a message called Custom Overwrite set pic voltage=%d on chain[%d] where the logs for bmminer starts after it finished booting.
The nice part of this firmware mod is that it should work with any version of bmminer, just replace the single-bard test file (and the interface files) on your regular firmware and is going to overclock voltage and freq, making it
easier for those antminer s9 versions which were not compatible with the open source firmware.
Alex