Hi Nathan,

Umbraco events will be your best friend with this.

https://our.umbraco.com/documentation/reference/events/ContentService-Events

So what you need to do is create a published event and target the parent. The one you are saving and publishing.

When the event fires you can then insert the doc type in code as usual.

To create an event look at the documentation in the above link. To summarize though.

1. Create a component for your published event
2. Then create a composer to tell Umbraco about your event.

Here is a copy of one of my published events. It doesn't do exactly what you need but it's half the way there.

private void ContentService_Published(IContentService sender, ContentPublishedEventArgs args)
        {
            try
            {
                foreach (var node in args.PublishedEntities)
                {
                    if (node.ContentType.Alias == "customRedirectsFolder")
                    {
                        CustomRedirectsFolder customRedirectsFolder = _siteHelper.GetPageById(node.Id) as CustomRedirectsFolder;
                        if (customRedirectsFolder != null)
                        {
                            if(customRedirectsFolder.ImportCsvfile != null)
                            {
                                _siteService.ImportCustomRedirects(node.Id, customRedirectsFolder.SkipRecords, customRedirectsFolder.TakeRecords, customRedirectsFolder.ImportCsvfile.Url);
                                node.Properties["importCSVFile"].SetValue(null);
                                sender.SaveAndPublish(node);
                            }
                            else if (customRedirectsFolder.ReRunDataFix)
                            {
                                List<CustomRedirect> customRedirects = _siteHelper.GetCustomRedirectsNeedFixing(node.Id);

                                if(customRedirects != null && customRedirects.Count() > 0)
                                {
                                    int count = 1;
                                    foreach(CustomRedirect customRedirect in customRedirects)
                                    {
                                        _siteService.ImproveCustomRedirect(customRedirect);

                                        count += 1;
                                    }
                                }

                                node.Properties["reRunDataFix"].SetValue(false);
                                sender.SaveAndPublish(node);
                            }
                        }
                    }
                }
            }
            catch (Exception e)
            {
                _logger.Error<PublishedEvent>("ContentService_Published | Exception: {0} | Message: {1}", e.InnerException != null ? e.InnerException.ToString() : "", e.Message != null ? e.Message.ToString() : "");
            }
        }

Regards

David