Preheat pellet smoker to 225°F for 10 to 15 minutes. Fill hopper with hickory, apple, cherry, or maple pellets.
Remove membrane from back of ribs if present. Cut racks into individual bones by slicing between each bone. You'll have 20 to 24 party ribs total.
Coat ribs with yellow mustard and season generously with BBQ rub on all sides. Let sit 10 to 15 minutes.
Place ribs on smoker grates with space between each piece. Smoke at 225°F for 1.5 to 2 hours until ribs develop mahogany color and bark looks set.
Make glaze: Combine brown sugar, honey, butter, BBQ sauce, vinegar, garlic powder, black pepper, and cayenne in saucepan. Heat until smooth and butter melts. Keep warm.
Transfer smoked ribs to foil pan. Pour glaze over ribs and toss to coat. Cover tightly with foil. Increase smoker to 250°F. Cook covered 45 to 60 minutes (50-55 minutes recommended).
Remove foil and toss ribs in glaze. Increase smoker to 275°F. Cook uncovered 15 to 25 minutes, stirring every 5 to 7 minutes, until glaze thickens and becomes glossy. Optional: brush with extra BBQ sauce last 5 minutes.
Rest 10 minutes. Serve hot from pan or transfer to platter. Drizzle remaining glaze over top.