If you shift to an Atkins-style diet you'll need less insulin. But you may still have high blood sugar reading occasionally, after a particularly rich meal, say, or because you really miss orange juice and decide to have some. And so you'll need to do some insulin adjustments.
Thing is, you have to adjust your adjustments too. If, pre-dietary adjustment, you needed x units of insulin to compensate for y extra carbohydrates, post-dietary adjustment you need < x units of insulin…and you have to figure out what that adjustment factor is.
This is from personal experience, not clinical trials.