Place the pork roast into a slow cooker, pour in the chicken broth, and add 2 cups water or enough to completely cover the roast. Mix in bouillon cubes, seasoned salt, Cajun seasoning, onion powder, and butter. Set cooker on Low and cook until the meat has fallen off the bone, 8 to 10 hours. Remove the meat from the broth and shred the pork with two forks; set the meat aside. Strain the broth through a fine-mesh strainer, discarding the bones; pour broth into a large pot and bring to a boil. Reduce heat to low and stir the shredded pork back into the broth. If desired, skim excess fat from broth with a large spoon. Stir in the bok choy, about 3/4 of the chopped cilantro leaves, and 1 cup water. Set aside remaining cilantro leaves for garnish. Simmer the soup while you prepare the rice noodles. Place rice noodles into a large bowl and cover with very hot tap water. Stir to separate the noodles and allow to soak until translucent, 25 to 30 minutes. Drain the noodles. To serve, place about 1/2 cup of rice noodles into a bowl and ladle the soup over the noodles. Sprinkle with reserved cilantro, crushed red pepper flakes, and Parmesan cheese to taste; serve with lime wedges.