It is easy to maintain in ketosis, without refeeds. As for really hard workouts, I've only recently ramped up on that (hour-long bike rides, sprinting 2x a week, actually running (trying to find exhaustion). But I've been very low carb, often keto for three years and, with moderate but not extreme workouts (15 minute stuff, sprints, bodyweight, lifting heavy things), have not regularly needed carb-ups. They do help soreness go away faster for me, though!
As for metabolism - without a sealed room and weeks to experiment in every season and controlling for every variable, you cannot know whether your metabolism is changing one bit.
Steak, eggs, potatoes - fruits, nuts, berries and forage. Coconut milk and potent herbs and spices. Tea instead of coffee now and teeny amounts of kelp daily. Let's see how this does! Not really had dairy much, and gut seems better for it.