In a bowl, whisk together the vinegar, juice, salt, and sugar until dissolved to make the brine. Add the peppercorns and the pork chops. Refrigerate for 12-24 hours.
Remove chops from brine, pat dry. Sprinkle with seasoning on all sides.
Preheat grill and place cast iron skillet on grate. Melt butter, add onions and garlic. Once soft, add brown sugar and apple juice. Bring to a boil and simmer until reduced by half. Add BBQ sauce, rum, five spice, and cinnamon. Continue to simmer until thick and syrup consistency.
Sear the pork chops on heated grill to mark the surface. Turn over and once internal temperature of the chops is above 130°F, mop with sauce. The pork chops are done once they reach 140°F-145°F internal temperature.