"Hey, I need to hack Fate!"

Okay, maybe you do.  I'm kind of vocally on the "minimum hack necessary" side, but we'll ignore that for a moment.  Here's what I recommend as a first step towards any Fate hack:

Imagine what you want to do.  Now, go write a scene, as in a short story or novel, that would use whatever you're trying to do.  Use this as your guide towards your hack.  As much as possible, when writing your modification/"system", try to keep the stuff in the system/rules matching up one to one with stuff in your fake scene.

When doing this, focus on the decisions that characters make (you know, the core of any story), what options they don't pursue, and how that impacts the scene and the hypothetical rest-of-the story.

If you need to write more than one scene, go for it.  But these scenes should provide good guidance for what you really need to have in your rules, what's extraneous detail, and what's utterly unnecessary.