[{"_id":"1234","Nodes":{"-14":{"_t":"DL","Key":"-14","Edges":[{"TargetNode":"-5"}],"Title":"Lookup","Text":"Data Lookup","ConnectionString":"Server=LOCALSERVER;Database=DataCache;User=sa;Password=1234;","TableName":"Customers","FieldMaps":[{"ID":2,"Column":"Name"},{"ID":1,"Column":"Number"}]}}}]

db.collection.update({},[{"$set":{"Nodes":{"$objectToArray":"$Nodes"}}},{"$set":{"Nodes":{"$map":{"input":"$Nodes","as":"n","in":{"$mergeObjects":["$$n",{"v":{"$mergeObjects":["$$n.v",{"ConnectionString":{"$replaceOne":{"input":"$$n.v.ConnectionString","find":"Server=LOCALSERVER","replacement":"Server=NEWSERVER"}}}]}}]}}}}},{"$set":{"Nodes":{"$arrayToObject":"$Nodes"}}}])