1. To prepare cups, weigh or lightly spoon masa harina into dry measuring cups; level with a knife. Combine masa, salt, and chile powder in a medium bowl, stirring with a whisk. Stir in 6 tablespoons warm water and 4 teaspoons melted butter; stir thoroughly to combine. Turn dough out onto a clean surface; knead lightly 1 minute. Cover dough; let rest 30 minutes.
2. Preheat oven to 400°.
3. Place dough on a sheet of plastic wrap; cover with another sheet of plastic wrap. Roll dough, still covered, to 1/8-inch thickness. Remove top sheet of plastic wrap. Cut 24 rounds from dough using a 2 1/2-inch round cutter. Coat 24 miniature muffin cups with cooking spray. Place 1 dough round in each muffin cup, gently pressing into bottom and up sides of cup. Bake at 400° for 14 minutes or until crisp and dry. Cool in pans on a wire rack. Remove corn cups from pans.
4. To prepare salad, combine chopped cooked shrimp, corn kernels, salsa verde, finely chopped celery, chopped green onions, and reduced-fat mayonnaise; cover with plastic wrap, and chill 20 minutes. Spoon 2 teaspoons salsa shrimp salad into each corn cup.