> db.clients.update({ _id: ObjectId("123")}, { $set: { _id: ObjectId("456")}})

Performing an update on the path '_id' would modify the immutable field '_id'

// store the document in a variable
doc = db.clients.findOne({_id: ObjectId("4cc45467c55f4d2d2a000002")})

// set a new _id on the document
doc._id = ObjectId("4c8a331bda76c559ef000004")

// insert the document, using the new _id
db.clients.insert(doc)

// remove the document with the old _id
db.clients.remove({_id: ObjectId("4cc45467c55f4d2d2a000002")})

db.status.find().forEach(function(doc){
    doc._id=doc.UserId; db.status_new.insert(doc);
});
db.status_new.renameCollection("status", true);

db.someCollection.find().snapshot().forEach(function(doc) {
   if (doc._id.indexOf("2019:") != 0) {
       print("Processing: " + doc._id);
       var oldDocId = doc._id;
       doc._id = "2019:" + doc._id;
       db.someCollection.insert(doc);
       db.someCollection.remove({_id: oldDocId});
   }
});

{
"_id":ObjectId("5b5ed345cfbce6787588e480"),
"title": "foo",
"description": "bar"
}

db.getCollection('myCollection').aggregate([
        {$match:
             {_id: ObjectId("5b5ed345cfbce6787588e480")}
        }
        {$project:
            {
             title: '$title',
             description: '$description'
            }
        },
        {$out: 'myCollection'}
    ])