Jason Fung puts it succinctly: “If you eat carbs you burn sugar, if you eat fat you burn fat”. Yes, once you get your metabolism into fat burn mode again, you will start to utilize onboard stored fat. It will happen by restricting carbs. Many will argue that you need to restrict calories on keto just as much as a CICO diet. But researchers are learning that keto does metabolic things to burn onboard fat that otherwise do not happen, so restricting calories is not necessarily so. Conversion of WAT to BAT, for example, where fat is converted directly to heat by mitochondrial uncoupling. Wasting energy, by converting fat to ketones and then excreting the ketones in urine and breath.
The primary danger of restricting calories is metabolic slowdown. The way to avoid this pitfal is to listen to your hunger. If you are hungry all the time, you need to eat more. If you are hungry only before your regular eating times, that’s OK, just your body’s way of telling you it’s time to eat. So, yes, you can increase your onboard fat burn if you do it right and not slow your metabolism. If you do it wrong you will lose the fat, but as soon as you start to eat you will regain it and probably then some. And you must start to eat again since you can not maintain an energy deficit forever or you’ll kill yourself.