Probably better to add carbs around the time the will be used up through training to avoid crashes ? No?
If you want to stay in ketosis, then carbs are not to be added. Humans can function just fine on ketones without crashes. If anything, adding carbs will make you "crash." When you train, your body will use the ketones for energy, not glucose. If you add glucose, ketosis will hault, you will burn through the glucose, and then have a crash before your body can go back into ketosis.
Doing a cyclical ketogenic diet just means you do a carb up once in a while, presumably to boost thyroid function. But there are numerous people out there who have been in ketosis for years, and have no symptoms of hypothyroidism. Look into work done by Dr. D'Agastino, he's on the forefront of ketosis research today. There are a few interviews you can look up on youtube which talk about his work with athletes, army/navy personnel, and regular folk.