Thaw the frozen precooked shrimp overnight in the refrigerator while still in its bag to collect the juices; alternatively, submerge the sealed bag in barely warm water until thawed.
Open the bag and drain the shrimp into a bowl, reserving the liquid; pat the shrimp dry with paper towels if they are very wet, then discard tails if present and cut shrimp into 1/2" pieces.
Pour the reserved shrimp liquid into a small saucepan and simmer until reduced by at least half to concentrate the flavor, watching closely so it does not burn; set aside to cool.
Bring a large pot of salted water to a boil and cook the macaroni according to package directions until tender but slightly firm (al dente); drain in a colander and allow to cool (do not rinse).
While the pasta cooks and cools, combine the diced shrimp, diced celery, and sliced green onions in a large bowl with a snap-on lid.
Prepare the dressing by mixing the reduced shrimp liquid with your preferred dressing ingredients (use only as much as needed for desired moistness).
When the macaroni is cool, add it to the shrimp mixture and gently fold in the dressing until evenly coated.
Season the salad with salt and pepper to taste, chill for a few hours if desired, and serve.
