Cut each hard boiled egg in half and place the yolks in a small bowl, and the whites on a serving plate.Add the Greek yogurt, dry mustard, hot sauce (and vinegar, if using), and blue cheese, and mash together with a fork, stirring until smooth. Season to taste with salt and pepper.Fill the egg white halves with the yolk mixture. Garnish with additional hot sauce and blue cheese, and sprigs of parsley or dill, if desired.Store in the refrigerator until ready to serve.