"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.
20140307 Hey I need to hack Fate’Okay mayb...
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Something I would like to add, that often comes up when trying to convert a rules heavy system, but not only then, is to ignore old rules and try to convert the setting, not the system. I've often seen this with magic systems, for example, which have some sort of mana/casting stress/backlash or other kind of system, not because the narrative supports it, but thats how magic is most often balanced in other games, and people feel like magic has to have something like it. The same trap lurks for many other things, and it's important to ask yourself if you are implementing a rule because it makes sense, or because all other systems you know do it like that.
tl/dr: "fiction first" ;)
For something like Savage Worlds or GURPS I'd recommend another approach.
I think your guidelines are good +Robert Hanz, because in going through that process I think it'd become pretty clear that, "Hey, I don't really need to hack anything. Fate Core just does this stuff already."
In the cases where it doesn't, then it gives a great guide as to what the rules need to actually do.
While I can understand the joy of creating a consistent mechanic (indeed they are often magic systems), it is kind of moot unless it is enabling a particular kind of story, which it may do by creating scarcity or hard choices, as Dark Sun does frinstance with despoiling