You mean a calf or cuff adjustment? Not seeing anything about a flex adjustment. Most write-ups talk about an adjustment to accommodate large calves.
This video talks about a "pinned cuff", which maybe is what you are referring to:
And found this discussion on the equivalent ladies model:
"with a fully-pinned cuff which is that true kind of race style, high-performance construction. Yeah, you can actually do a couple things which is neat. You can actually remove the pin in the back and you can put a urethane plug in and it gives the boot more progressive flex or, if you leave it in, the boot has more response, more power, better snap and drive through that turn." Edited by sibhusky - 11/1/15 at 9:50am