public void SetName( 
   string name
)

//Modify an element's name.

//Perform on the worker thread
await QueuedTask.Run(() =>
{
  element.SetName("New Name");
});

//Must be on QueuedTask.Run(() => { ...

//Build geometry
Coordinate2D ll = new Coordinate2D(6, 2.5);
Coordinate2D ur = new Coordinate2D(8, 4.5);
Envelope env = EnvelopeBuilderEx.CreateEnvelope(ll, ur);

//Reference MF, create legend and add to layout
MapFrame mf = layout.FindElement(mapFrameName) as MapFrame;
var surroundInfo = new LegendInfo()
{
  MapFrameName = mf.Name
};

var legendElm = ElementFactory.Instance.CreateMapSurroundElement(
  layout, env.Center, surroundInfo) as Legend;
legendElm.SetName("New Legend");

//Must be on QueuedTask.Run(() => { ...

//Build geometry
Coordinate2D center = new Coordinate2D(7, 5.5);

//Reference a North Arrow in a style
StyleProjectItem stylePrjItm = Project.Current.GetItems<StyleProjectItem>()
                               .FirstOrDefault(item => item.Name == "ArcGIS 2D");
NorthArrowStyleItem naStyleItm = stylePrjItm.SearchNorthArrows(
                                       "ArcGIS North 10")[0];

//Reference MF, create north arrow and add to layout 
//var mf = container.FindElement("New Map Frame") as MapFrame;
var mf = layout.FindElement(MapFrameName) as MapFrame;
var narrow_info = new NorthArrowInfo()
{
  MapFrameName = mf.Name,
  NorthArrowStyleItem = naStyleItm
};
var arrowElm = (NorthArrow)ElementFactory.Instance.CreateMapSurroundElement(
  layout, center.ToMapPoint(), narrow_info) as NorthArrow;
arrowElm.SetName("New North Arrow");
arrowElm.SetHeight(1.75);
arrowElm.SetX(7);
arrowElm.SetY(6);

//Update an element's properties.

//Performed on worker thread
QueuedTask.Run(() =>
{
  // update an element's name
  element.SetName("New Name");

  // update and element's visibility
  element.SetVisible(true);
});