Heat a heavy-bottomed skillet over medium heat. Working in batches, add dried peppers to skillet and toast lightly for 3 to 4 seconds on each side. Transfer toasted chiles to a medium bowl. Cover with hot water and let stand until soft, about 10 to 15 minutes.
Transfer peppers to the jar of a blender or bowl of a food processor, along with olive oil, garlic, cumin, oregano, aniseed, paprika, orange juices, guava preserves or honey, sherry, brown loaf sugar, and salt; blend until smooth.
Place bacon in a 2-inch deep baking pan. Pour the chile mixture over bacon and rub thoroughly until fully coated. Cover with plastic wrap and let marinate at least 6 hours and up to overnight.
Preheat oven to 350 degrees with rack in the center. Remove plastic wrap from baking dish and add 1/4 cup water to dish. Cover baking dish tightly with parchment paper-lined aluminum foil. Transfer baking dish to oven and bake for 1 hour. Continue baking and basting bacon, until golden brown and fork tender, about 20 minutes more.
Transfer bacon to a large cutting board and cut into 2 1/2-inch pieces. Serve immediately with Guatemalan red cabbage relish or Mendoza's fresh corn polenta; garnish with cacao nibs, if desired.