Place the unwrapped blocks of cheese on a wire rack. (If the outside temperature is hot, then you can place the wire rack on top of a baking sheet with ice cubes in a single layer to help keep the cheese cooler while it smokes.)
Fill a smoke tube with wood pellets of your choice. Light the smoke tube and place it on one side of the pellet grill or smoker with the grill turned off. Place the wire rack with cheese on the opposite side of the grill. Close the lid and cold smoke the blocks of cheese for 1.5 - 2.5 hours, based on your desired smokiness. Then, remove the smoked cheese from the grill.
Shred the smoked cheeses and mix together in a large bowl. Separate the shredded cheese into 3 equally-sized piles.
While the cheese is smoking, boil a pot of water and cook the pasta according to package instructions, just until it is al dente. Drain the pasta and allow it to cool down.
Make the roux. In a large saucepan over medium-low heat, melt half a stick of butter. When the butter is melted, add the flour and whisk continuously for about 2-3 minutes while the flour cooks. Slowly pour in the milk, whisking constantly, until the mixture is smooth.
Continue to cook an additional 2-4 minutes, or until the the mixture has thickened slightly. Then, stir in the softened cream cheese and continue to cook until the cheese is fully melted in the sauce.
Add all of the spices including garlic powder, ground mustard, paprika, salt, pepper, and cayenne pepper to the sauce. Stir to combine. Then, add about one-third of the shredded smoked cheeses, reserving the remaining for later. Stir to melt the cheeses until the cheese sauce is completely smooth.
In a large bowl, add the cooled cooked pasta and about one-third of the shredded cheese. Toss to combine. Then, pour about 80% of the cheese sauce into the bowl with the pasta and cheese. Stir to combine.
Butter the bottom and sides of a 9x13 baking dish. Spread the pasta and cheese sauce mixture into the prepared baking dish.
Optional - Make the crispy topping. Combine ½ stick melted butter, panko breadcrumbs, grated parmesan, and chopped bacon (optional) in a medium bowl. Stir to combine.
Pour the remaining cheese sauce on top of the baking dish. Sprinkle with the remaining one-third of shredded cheese, and lightly mix it into the sauce on top. Evenly distribute the crispy topping on top of the dish.
Place the mac and cheese on the pellet grill uncovered, and smoke at 250℉ for about 45 minutes. Then, increase the grill temperature to 325℉ and cook for an additional 15-20 minutes, or until the top is lightly golden brown and the cheese is bubbly.
Remove from the grill and allow to cool about 10 minutes before serving.