Preheat a smoker to 250°F. Combine the cooked macaroni, milk, and ½ cup of the cheddar in a bowl. Set the filling aside.

In a large bowl, mix the ground beef, ground pork, breadcrumbs, egg, onion, salt, pepper, and smoked paprika. Stir just until combined to keep the meatloaf tender.

Lay a sheet of parchment on a work surface. Shape the meat mixture into a rectangle about ¾ inch thick. Spoon the macaroni mixture down the center, leaving a border around the edges.

Use the parchment to help fold the meat mixture over the filling. Pinch the seam and ends closed, then place the loaf seam-side down on a wire rack or smoker-safe tray.

Stir the brown sugar and apple cider vinegar into ½ cup of the barbecue sauce. Brush half of this glaze over the meatloaf.

Smoke the loaf until its center reaches 160°F, checking the temperature with an instant-read thermometer. Brush on the remaining glaze during the final 20 minutes of cooking. Sprinkle the remaining ¼ cup cheddar over the top for the last few minutes, until melted.

Remove the meatloaf from the smoker and let it rest for 10 minutes before slicing. Serve with the remaining ¼ cup barbecue sauce on the side.