Preheat the oven to 250°. In a bowl, mix 1/4 cup of the sugar with the garlic salt, chile powder, salt, black pepper, celery salt, cayenne, cinnamon and white pepper. Transfer 1 tablespoon of the spice mix to a medium bowl and whisk in the cider, apple jelly, honey and the remaining 1/4 cup of sugar.
Pull the membrane off the underside of each rib rack using a towel to grasp the corner. On a rimmed baking sheet, rub the ribs with the remaining spice mix; bake, meaty side up, for 2 1/2 hours. Pour the cider mixture over the ribs and turn to coat. Tightly cover with foil and bake for 1 hour.
Light a grill. Uncover the ribs and brush with the barbecue sauce; grill over moderate heat, turning and brushing, until glazed, 15 minutes. Let rest for 10 minutes, then cut between the bones and serve.