public int ID {get; set;}

//Control points are special vertices used to apply symbol effects to line or polygon features.
  //By default, they appear as diamonds when you edit them.
  //They can also be used to migrate representations from ArcMap to features in ArcGIS Pro.
  await QueuedTask.Run(() =>
  {
    var changeVertexIDOperation = new EditOperation();
    //iterate through the points in the polyline.
    var lineLayerCursor = lineLayer.GetSelection().Search();
    var lineVertices = new List<MapPoint>();
    long objectId = -1;
    while (lineLayerCursor.MoveNext())
    {
      var lineFeature = lineLayerCursor.Current as ArcGIS.Core.Data.Feature;
      var line = lineFeature.GetShape() as Polyline;
      int vertexIndex = 1;
      objectId = lineFeature.GetObjectID();
      //Each point is converted into a MapPoint and gets added to a list. 
      foreach (var point in line.Points)
      {
        MapPointBuilderEx mapPointBuilderEx = new(point);
        //Changing the vertex 6 and 7 to control points
        if (vertexIndex == 6 || vertexIndex == 7)
        {
          //These points are made "ID Aware" and the IDs are set to be 1.
          mapPointBuilderEx.HasID = true;
          mapPointBuilderEx.ID = 1;
        }

        lineVertices.Add(mapPointBuilderEx.ToGeometry() as MapPoint);
        vertexIndex++;
      }
    }
    //create a new polyline using the point collection.
    var newLine = PolylineBuilderEx.CreatePolyline(lineVertices);
    //edit operation to modify the original line with the new line that contains control points.
    changeVertexIDOperation.Modify(lineLayer, objectId, newLine);
    changeVertexIDOperation.Execute();
  });
}

{
  // MapPointBuilderEx constructors can run on any thread.

  MapPoint point1 = null;
  MapPoint point2 = null;

  SpatialReference spatialReference = SpatialReferenceBuilder.CreateSpatialReference(54004);

  MapPointBuilderEx mapPointBuilder = new MapPointBuilderEx(100, 200, spatialReference);
  SpatialReference sr = mapPointBuilder.SpatialReference; // sr != null
  int wkid = sr.Wkid; // wkid = 54004
  bool hasZ = mapPointBuilder.HasZ;   // hasZ = false
  bool hasM = mapPointBuilder.HasM;   // hasM = false
  bool hasID = mapPointBuilder.HasID; // hasID = false
  bool isEmpty = mapPointBuilder.IsEmpty; // isEmpty = false
  double x = mapPointBuilder.X;   // x = 100
  double y = mapPointBuilder.Y;   // y = 200
  double z = mapPointBuilder.Z;   // z = 0, default value
  double m = mapPointBuilder.M;   // m is NaN, default value
  double id = mapPointBuilder.ID; // id = 0, default value

  // Do something with the builder
  mapPointBuilder.Z = 12; // Setting the z-value automatically sets HasZ property to true

  point1 = mapPointBuilder.ToGeometry();
  sr = point1.SpatialReference; // sr != null
  wkid = sr.Wkid; // wkid = 54004
  hasZ = point1.HasZ;   // hasZ = true
  hasM = point1.HasM;   // hasM = false
  hasID = point1.HasID; // hasID = false
  x = point1.X;   // x = 100
  y = point1.Y;   // y = 200
  z = point1.Z;   // z = 12
  m = point1.M;   // m is NaN, default value
  id = point1.ID; // id = 0, default value

  // Change some of the builder properties
  mapPointBuilder.SetValues(11, 22);
  mapPointBuilder.HasZ = false;
  mapPointBuilder.HasM = true;
  mapPointBuilder.M = 44;

  // Create another point
  point2 = mapPointBuilder.ToGeometry();

  bool isEqual = point1.IsEqual(point2); // isEqual = false

  // Set the builder to empty
  // Sets X and Y to NaN. Sets other attributes to the default values.
  // Does not change the attribute awareness.
  mapPointBuilder.SetEmpty();

  MapPoint point3 = mapPointBuilder.ToGeometry();
  sr = point3.SpatialReference; // sr != null
  wkid = sr.Wkid; // wkid = 54004
  hasZ = point3.HasZ;        // hasZ = false
  hasM = point3.HasM;        // hasM = true
  hasID = point3.HasID;      // hasID = false
  isEmpty = point3.IsEmpty;  // isEmpty = true
  x = point3.X;              // x is NaN
  y = point3.Y;              // y is NaN
  z = point3.Z;              // z = 0, default value
  m = point3.M;              // m is NaN, default value
  id = point3.ID;            // ID = 0, default value

  // Create a builder from a point
  mapPointBuilder = new MapPointBuilderEx(point2); // point1 = (11, 22, 0, 44, 0)
  sr = mapPointBuilder.SpatialReference; // sr != null
  wkid = sr.Wkid; // wkid = 54004
  hasZ = mapPointBuilder.HasZ;        // hasZ = false
  hasM = mapPointBuilder.HasM;        // hasM = true
  hasID = mapPointBuilder.HasID;      // hasID = false
  isEmpty = mapPointBuilder.IsEmpty;  // isEmpty = false
  x = mapPointBuilder.X;              // x = 11
  y = mapPointBuilder.Y;              // y = 22
  z = mapPointBuilder.Z;              // z = 0, default value
  m = mapPointBuilder.M;              // m = 44
  id = mapPointBuilder.ID;            // ID = 0, default value

  // Setting attribute values automatically sets the corresponding flag to true
  mapPointBuilder.Z = 150;
  mapPointBuilder.ID = 2;

  // Remove the spatial reference
  mapPointBuilder.SpatialReference = null;

  MapPoint point4 = mapPointBuilder.ToGeometry() as MapPoint;
  sr = point3.SpatialReference; // sr = null
  hasZ = point3.HasZ;        // hasZ = true
  hasM = point3.HasM;        // hasM = true
  hasID = point3.HasID;      // hasID = true
  isEmpty = point3.IsEmpty;  // isEmpty = false
  x = point3.X;              // x = 11
  y = point3.Y;              // y = 22
  z = point3.Z;              // z = 150
  m = point3.M;              // m = 44
  id = point3.ID;            // ID = 2
}