Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally until cooked through but firm to the bite, 8 minutes. Drain.
Mix macaroni, mushroom soup, ham, milk, and Cheddar cheese in a bowl; fold in diced hard-boiled eggs. Spoon mixture into a 9x13-inch casserole dish. Cover dish with plastic wrap and refrigerate 8 hours to overnight.
Preheat oven to 350 degrees F (175 degrees C). Remove plastic wrap from dish.
Bake in the preheated oven for 30 minutes; layer sliced hard-boiled eggs on top of casserole. Bake until casserole is cooked through and bubbling, about 10 more minutes.
