Bring a large pot of water to a rolling boil. Add macaroni and cook until al dente (7-8 minutes). Drain in colander and rinse with cold water. Transfer noodles to a large bowl. Cover the bowl with plastic wrap or a lid and refrigerate until completely cool.
Add peas or edamame, sliced celery, scallions, and ham (if desired) and toss to blend.
In small bowl or 4-cup measure, whisk together light mayonnaise, sour cream, vinegar, sugar, nutmeg, and 1/4 teaspoon salt (if desired). Spoon over macaroni mixture and stir to blend. Season with pepper to taste. Cover bowl and refrigerate until ready to serve.