public class VertexSymbolOptions 

/// <summary>
/// Within the specialization of a MapTool, this method handles activation and deactivation of the tool, allowing customization of sketch segment and vertex symbology when
/// the tool becomes active.  When the tool is activated, this method customizes the appearance of sketch segments and vertices by updating their symbol options. This includes setting colors, widths, marker types, and other visual properties for both segments and regular unselected vertices.
/// </summary>
protected override Task OnToolActivateAsync(bool active)
{
  QueuedTask.Run(() =>
  {
    //Getting the current symbology options of the segment
    var segmentOptions = GetSketchSegmentSymbolOptions();
    //Modifying the primary and secondary color and the width of the segment symbology options
    var deepPurple = new CIMRGBColor() { R = 75, G = 0, B = 110 };
    segmentOptions.PrimaryColor = deepPurple;
    segmentOptions.Width = 4;
    segmentOptions.HasSecondaryColor = true;
    var pink = new CIMRGBColor() { R = 219, G = 48, B = 130 };
    segmentOptions.SecondaryColor = pink;
    //Creating a new vertex symbol options instance with the values you want
    var vertexOptions = new VertexSymbolOptions(VertexSymbolType.RegularUnselected);
    var yellow = new CIMRGBColor() { R = 255, G = 215, B = 0 };
    var purple = new CIMRGBColor() { R = 148, G = 0, B = 211 };
    vertexOptions.AngleRotation = 45;
    vertexOptions.Color = yellow;
    vertexOptions.MarkerType = VertexMarkerType.Star;
    vertexOptions.OutlineColor = purple;
    vertexOptions.OutlineWidth = 3;
    vertexOptions.Size = 5;

    //Setting the value of the segment symbol options
    SetSketchSegmentSymbolOptions(segmentOptions);
    //Setting the value of the vertex symbol options of the regular unselected vertices using the vertexOptions instance created above.
    SetSketchVertexSymbolOptions(VertexSymbolType.RegularUnselected, vertexOptions);
  });

  return base.OnToolActivateAsync(active);
}

{
  var options = ApplicationOptions.EditingOptions;
  await QueuedTask.Run(() =>
  {
    //There are 4 vertex symbol settings - selected, unselected and the
    //current vertex selected and unselected.
    var reg_select = options.GetVertexSymbolOptions(VertexSymbolType.RegularSelected);
    var reg_unsel = options.GetVertexSymbolOptions(VertexSymbolType.RegularUnselected);
    var curr_sel = options.GetVertexSymbolOptions(VertexSymbolType.CurrentSelected);
    var curr_unsel = options.GetVertexSymbolOptions(VertexSymbolType.CurrentUnselected);

    //to convert the options to a symbol use
    //GetPointSymbol
    var reg_sel_pt_symbol = reg_select.GetPointSymbol();
    //ditto for reg_unsel, curr_sel, curr_unsel
  });
}

{
  var options = ApplicationOptions.EditingOptions;
  //var options = ApplicationOptions.EditingOptions;
  await QueuedTask.Run(() =>
  {
    //change the regular unselected vertex symbol
    //default is a green, hollow, square, 5pts. Change to
    //Blue outline diamond, 10 pts
    var vertexSymbol = new VertexSymbolOptions(VertexSymbolType.RegularUnselected);
    vertexSymbol.OutlineColor = ColorFactory.Instance.BlueRGB;
    vertexSymbol.MarkerType = VertexMarkerType.Diamond;
    vertexSymbol.Size = 10;

    //Are these valid?
    if (options.CanSetVertexSymbolOptions(
         VertexSymbolType.RegularUnselected, vertexSymbol))
    {
      //apply them
      options.SetVertexSymbolOptions(VertexSymbolType.RegularUnselected, vertexSymbol);
    }
  });
}

{
  var options = ApplicationOptions.EditingOptions;
  //var options = ApplicationOptions.EditingOptions;
  await QueuedTask.Run(() =>
  {
    //ditto for reg selected and current selected, unselected
    var def_reg_unsel =
      options.GetDefaultVertexSymbolOptions(VertexSymbolType.RegularUnselected);
    //apply default
    options.SetVertexSymbolOptions(
      VertexSymbolType.RegularUnselected, def_reg_unsel);
  });
}