public virtual void SetDefinition( 
   CIMElement cimElement
)

{
  //Set the CIM halo properties of a north arrow.

  //Reference the first selected north arrow element
  var northArrow = LayoutView.Active.GetSelectedElements().OfType<NorthArrow>().First();

  //Note: Must be on QueuedTask.Run
  //Get definition of north arrow...
  var cim = northArrow.GetDefinition() as CIMMarkerNorthArrow;

  //this halo symbol is 50% transparent, no outline (i.e. 0 width)
  //First construct a polygon symbol to use in the Halo
  //Polygon symbol will need a fill and a stroke
  var polyFill = SymbolFactory.Instance.ConstructSolidFill(ColorFactory.Instance.CreateRGBColor(0, 0, 0, 50));
  var polyStroke = SymbolFactory.Instance.ConstructStroke(ColorFactory.Instance.BlackRGB, 0);
  var haloPoly = SymbolFactory.Instance.ConstructPolygonSymbol(polyFill, polyStroke);

  //Set the north arrow definition of HaloSymbol and HaloSize 
  ((CIMPointSymbol)cim.PointSymbol.Symbol).HaloSymbol = haloPoly;
  ((CIMPointSymbol)cim.PointSymbol.Symbol).HaloSize = 3;//size of the halo

  //Apply the CIM changes back to the element
  northArrow.SetDefinition(cim);
}

{
  // The Locked property is displayed in the TOC as a lock symbol next
  // to each element.  If locked the element can't be selected in the layout
  // using the graphic selection tools.
  //Note: Must be on QueuedTask.Run

  //Reference an element 
  if (element != null)
  {
    // Modify the Locked property via the CIM
    CIMElement CIMElement = element.GetDefinition() as CIMElement;
    CIMElement.Locked = true;
    element.SetDefinition(CIMElement);
  }
}

{
  //Apply a background color to the map frame element using the CIM.
  //Note: Must be on QueuedTask.Run
  //Get the map frame's definition in order to modify the background.
  var mapFrameDefn = mapFrame.GetDefinition() as CIMMapFrame;

  //Construct the polygon symbol to use to create a background
  var polySymbol = SymbolFactory.Instance.ConstructPolygonSymbol(
                  ColorFactory.Instance.BlueRGB, SimpleFillStyle.Solid);

  //Set the background
  mapFrameDefn.GraphicFrame.BackgroundSymbol =
                                    polySymbol.MakeSymbolReference();

  //Set the map frame definition
  mapFrame.SetDefinition(mapFrameDefn);
}