Usually, no matter how many "toggles" you may throw in as optional, what you do is playtest for certain specific pre-sets. I.e. "Does the 'default D&D experience' flow nicely enough? What about the super-hard mode? Is it still reasonably doable?".
You don't need to test extensively every possible combination, nor to worry if the super-easy mode is "just super easy" or "super-super-easy" because chances are that the people who picked that option are not interested in having anything resembling a decent challenge to begin with.
If you have a "food-as-resource" system, you playtest to learn how well it works and finely it needs to be tuned, there's no need to investigate how much easier the game gets disabling that feature, because clearly whoever will pick that option is not interested in maintaining things challenging anyway.
And so on.
