[{"values":[{"number1":5,"number2":6,"anotherProp":"...","anotherProp2":"..."},{"number1":8,"number2":1,"anotherProp":"...","anotherProp2":"..."}]}]

db.collection.aggregate([{$project:{values:{$map:{input:"$values",as:"v",in:{"$mergeObjects":[{sum:{$add:["$$v.number1","$$v.number2"]}},"$$v"]}}}}}])