Spatchcock the chicken, and place it on a wire cooling rack set on top of a baking sheet with the breasts facing up. Pat dry with paper towels. Sprinkle all sides of the chicken with kosher salt. Refrigerate the chicken on the wire rack/baking sheet for 12-24 hours.
Make the injection liquid. Combine the canned pickled jalapeno juice, Tajin hot sauce, and lime juice in a bowl and mix well.
Inject the chicken. Using a meat injector syringe, draw up the jalapeño-lime injection liquid into the syringe barrel. Insert the needle of the injector into various parts of the chicken, such as the breast, thighs, and drumsticks, pushing the plunger slowly to release the injection liquid as you withdraw the needle. Repeat the process in multiple spots across the chicken to ensure thorough distribution of the injection. *TIP - Try to limit the number of holes in the chicken skin - Use the same holes, but adjust the angle of the injector to reach different areas of them meat.
Refrigerate the injected chicken on the wire rack/baking sheet combo for about 4-4.5 hours.
Make the seasoning blend. Combine all Mexican seasoning ingredients in a medium bowl and mix well.
After the chicken has rested in the refrigerator, spray with duck fat spray or rub a thin layer of oil all over as a binder. Sprinkle liberally with the Mexican seasoning blend.
Preheat the grill to about 180-225℉ with your choice of wood pellets. *If your pellet grill has a "super smoke" mode, turn that on.
Smoke the whole chicken at the lower 180-225°F temperature for about 1 hour. Then, adjust the temperature of the grill up to about 325-350°F. Continue to cook the chicken until the thickest part of the breasts reaches 165°F (as checked with an instant read meat thermometer). The total cook time at the higher 325-350°F temp could be 2-3 hours depending on the size of your chicken and the temperature of your grill.
When the chicken is cooked through, remove from the grill and allow to rest for about 30-45 minutes, or until the internal temperature has dropped to about 145°F. Then, slice or shred and serve. *You can also add the shredded chicken to a Ziploc bag and refrigerate overnight to use for Mexican dishes the next day.