Reduce s9/t9 frequency and power usage

[cableiso]

I have some s9's on the way but I'd like to run them at a lower frequency.  Looks like this USED to be possible from the manual I downloaded but now all the firmware are auto-frequency?

So anyone know how to hack it or downgrade to an old firmware that allows manual setting?  Again, I am not OC'ing  - I'd like to underclock for lower draw and presumably longer lifetime.

[cableiso]

OK, I would like to refine my question because if I can use cgminer, I'll just set frequency in the conf.

So I see an open source cgminer for s9 on github.  Is this the software that comes on the s9, or if not - how do I get it on there?

Then, am I thinking correctly that I can change the clocks just by changing the conf file?