Database
[{"execution":{"test_split":0,"artifacts":{"9ed39_output":{"uri":"http://100.com/somefile"},"8d777_output":{"uri":"http://100.com/anotherfile"}}}}]
Query
db.collection.aggregate([{$set:{"execution.artifacts":{$objectToArray:"$execution.artifacts"}}},{$set:{"execution.artifacts":{$map:{input:"$execution.artifacts",in:{k:"$$this.k",v:{uri:{$replaceOne:{input:"$$this.v.uri",find:"100.",replacement:"200."}}}}}}}},{$set:{"execution.artifacts":{$arrayToObject:"$execution.artifacts"}}},])