[{nId:0,children0:[{nId:3,access:[{permission:"view",email:"user1@email.com"}]},{nId:4,access:[{permission:"view",email:"user2@email.com"}]}]}]

db.collection.aggregate([{"$addFields":{"children0":{"$map":{"input":"$children0.access","as":"accessInfo","in":{"$cond":[{"$eq":["$$accessInfo.email","user1@email.com"]},{"$mergeObjects":["$$accessInfo",{"hasAccess":true}]},{"$mergeObjects":["$$accessInfo",{"hasAccess":false}]},]}}}}}])