Start by cutting the pork butt into cubes. Place in a large pot and cover with 6 quarts of cool water. Bring to a boil over high heat, stirring occasionally. Reduce heat to medium-low and simmer for 1 hour or until tender.
Strain the pork cubes, reserving both the meat and cooking liquid separately in separate containers. In a large mixing tub, mix together the pork cubes, black pepper, parsley, green onion slices, cooked white long-grain rice, chicken livers, and celery.
Heat the reserved cooking liquid in a pan over medium heat. Add in the chopped onions, bell peppers, garlic, salt, and cayenne. Simmer for 10 minutes until the vegetables are tender.
Add the cooked vegetables to the pork mixture and stir to combine. Using a grinder, process the pork and vegetable mixture in batches until finely ground. Fill casings with the mixture and twist to form boudin. Refrigerate until ready to cook.