Dry the pork shoulder and season all over with salt. Melt the lard in a large saucepan, Dutch oven, or 6-quart pressure cooker. Add the pork belly, lard, onion, orange, Coca-Cola, chiles, cumin, and 3 tablespoons salt. Bring the liquid to a simmer, cover, and cook over low heat for 4 hours, or until very tender and easily shredded with a fork (if using a pressure cooker, cook on high for 90 minutes). Let cool, then pour off the fat, reserving 1 cup of lard for crisping the pork (by all means, save the leftover lard for another use). Discard the pork skin, bone, and aromatics.