XMP Metadata - I want to edit the XMP metadata while persevering any other metadata.

private static void AddMediaIdToImage(string imagePath, string mediaId)
{
            XmpData xmp = null;
            string dir = Path.GetDirectoryName(imagePath);
            string file = Path.GetFileNameWithoutExtension(imagePath);
            file += "(2).jpg";
            file = Path.Combine(dir, file);

            using (var jpegReader = new JpegReader(imagePath))
            using (var jpegWriter = new JpegWriter(file))
            {
                xmp = new XmpData();

                //Check if XMP data are present in the file and...
                if (jpegReader.Xmp != null)
                {
                    //...get an XML code from the reader
                    xmp = new XmpData(jpegReader.Xmp);
                }
                else
                {
                    //...or create an empty structure
                    xmp = new XmpData();
                }

                var ns = XmpNamespace.AddNamespace("http://photoboothsupplyco.com/", "pbsco:");
                var node = new XmpValueNode(XmpNodeType.SimpleProperty, mediaId, ns, "pbsco:mediaId");
                xmp.AddNode(node);

                jpegWriter.Xmp = xmp.Save();
                Pipeline.Run(jpegReader+jpegWriter);
            }
 }