void SetXml( 
   string xml
)

await QueuedTask.Run(() =>
{
    var xml = System.IO.File.ReadAllText(@"E:\Data\Metadata\MetadataForFeatClass.xml");
    //Will throw InvalidOperationException if the metadata cannot be changed
    //so check "CanEdit" first
    if (featureClassMetadataItem.CanEdit())
        featureClassMetadataItem.SetXml(xml);
});