Overclock S9 is possible. Note you will damage your chips if you get wrong and will kill miner!
Best to leave set at standard with overclocking issues can show more HW/Error /Reject +more issue can happen.
Stick to standard unless you are feeling brave.
Asicworld
I have previous experience with overclocking CPUs and GPUs. I think that I have all prereuisits for overclocking - reliable 2000W power supply, cold place (15 Celsius degree or less) where the minner is placed. I will monitor the temperature of the chips and fan speeds.
My main fear is Do I have a way to return the old frequency to the device in case it does not work?
For example when I overclock CPUs I can make hardware reset with jumpers of the motherboard bios setting. As result the device start wotking normally with default settings.
Can I do the same with AntMiner or if the configuration is wrong the whole miner will die without way to restore default configuration?
Yes there is a reset that can restore default your s9 miner you can found the reset near to ethernet but first you need to wait for 2 minutes afte bootup before you can reset it tp default config..
There is also other way to reset that can be called soft reset just login to control panel and goto upgrade you can see the reset to default and perform the reset..
Hope that it can help you to reset your hardware if ever you made a wrong setup then just do a reset... make sure that everything is fixed in the socket because there are sometimes having a firmware fault when resetting..