This feature is implemented in the latest version of
Awesome Miner.
The benefit of using Awesome Miner for this is that you can easily define schedules and rules for when this operation should be performed. It can be performed for one, many or all your Antminers - no need to manually go into each Antminer and make changes (that's boring if you have more than a single Antminer).
Please see this help page for instructions how to use the Rule concept in Awesome Miner to define schedules for changing the frequency of Antminer S7 / S9.
http://www.awesomeminer.com/help/antmineroperations.aspxBecause this implementation is based on the Awesome Miner rules, you can define way more advanced conditions when to trigger a change. For example when the temperature is above a certain limit or when the HW Error rate is getting too high.