Preheat the oven to 375 degrees F. Line a shallow roasting pan with foil and set aside.
For the blackening spice: In a bowl stir together the dark chili powder, garlic powder, onion powder, red pepper flakes, paprika, salt, celery powder, dried parsley, dried thyme and cayenne pepper. Store in an airtight container. Yield: 2/3 cup.
For the lemon pepper seasoning: In a bowl, stir together the pepper, dried lemon peel, dried minced onion, dried thyme, coriander seeds and sugar if using. Store in an airtight container. Yield: 1 1/4 cups.
For the game hens: Sprinkle one of the game hens all over with 2 tablespoons blackening spice. Sprinkle another game hen all over with 2 tablespoons lemon pepper seasoning. Sprinkle the third all over with the rosemary and thyme, garlic, and some salt and pepper. Place the game hens, breast-side up, in the pan; twist the wing tips under the backs.
Roast, uncovered, until an instant-read thermometer inserted into the thigh of each hen registers 180 degrees F, 1 hour to 1 hour 15 minutes. Remove from the oven and let rest for 5 to 7 minutes before serving.