Preheat the oven to 375°F (190°C). Season the whole chicken pieces with salt and pepper.
Heat 1 tablespoon of vegetable oil in a large heavy pot or Dutch oven over medium-high heat. Brown the chicken on all sides, about 3 minutes per side.
Add 1 cup water, 1/2 tsp cumin, 1/2 tsp garlic powder, 1 tsp chile powder, and 1/2 tsp red chile flakes to the pot. Cover and transfer the pot to the oven; bake until the chicken is cooked through, about 20–25 minutes.
Remove the chicken from the pot, reserving the cooking juices, and let cool until easy to handle. Discard any bones and skin if present, then finely shred the meat.
Return the pot with the reserved juices to the stovetop over medium-high heat and simmer until the liquid is reduced by about half. Transfer the reduced pan sauce to a heat-proof dish and let it cool slightly; skim off excess fat if desired.
In a large bowl, combine the shredded chicken, chopped green chiles, thawed corn, diced red onion, minced garlic, shredded cheese, and the additional spices: 1/2 tsp cumin, 1/2 tsp garlic powder, 1 tsp chile powder, and 1 tsp black pepper. Add 1/2 to 2/3 cup of the reduced pan sauce to moisten, then toss until evenly combined.
Warm about 1/4 cup of the vegetable oil in a large skillet over medium heat until shimmering. Place about 2 tablespoons of the chicken filling near one edge of each tortilla and roll tightly; secure with a toothpick if needed.
Working in 4 batches, add fresh oil (about 1/4 cup) for each batch, and pan-fry the flautas until golden brown and heated through, about 3 minutes per side. Wipe the pan between batches if necessary.
Drain the cooked flautas on paper towels, then transfer to a platter and serve warm with sour cream and guacamole.