You can sort of do this... but there is a catch:
Gearing Strategies created via our simulator represent a cohesive statistical method: they take your simulation data and create a model that can very quickly predict the simulated value of any set of gear. This allows us to sift through billions of sets of gear very quickly and do all the convenient features like Best in Bags.
You can't "hand-tweak" these strategies. Doing so would essentially "break" the promise that they will predict simulation results well. It can also have very weird side effects when you start hand-tweaking them, and result in wacky gear rankings.
There is another kind of strategy that you can make, called an "Imaginary Strategy" -- where you tell us exactly how much everything is worth to you. There is a post about it here: http://forums.askmrrobot.com/t/imaginary-strategies/1722
With this, you can set caps on stats and things like that, but you also need to tell the optimizer how to rank everything else in relation to your stats (trinkets, legendaries, set bonuses, etc.).
Our built-in "Adaptive" gearing strategies do not support any kind of hand-modification of stat values and the such. (We don't have one for Brewmaster yet, but it is coming very soon! In the next 1-2 weeks.) They are like a supercharged version of a custom Gearing Strategy created via our simulator, and are heavily tuned to ensure that they predict well across a wide range of gear.
If you are trying to reach a haste threshold, our suggestion would be to first examine why you want to reach that haste threshold. Then we could go to the Brewmaster simulator and test the impact of that theory, and determine if the new Adaptive gearing strategy just handles it "out of the box", or if it's not that impactful, or if some other kind of simulation is required to measure the value of it.
Or of course, make one of the super-flexible Imaginary Strategies that can do almost anything. But they are a bit labor-intensive for most users.