public void Reshape( 
   SelectionSet features,
   Geometry reshapeGeometry
)

// Reshapes the specified feature in the given feature layer.
await QueuedTask.Run(() =>
  {
    var reshapeFeatures = new EditOperation() { Name = "Reshape Features" };

    reshapeFeatures.Reshape(featureLayer, objectId, modifyLine);

    //Reshape a set of features that intersect some geometry....

    reshapeFeatures.Reshape(MapView.Active.GetFeatures(modifyLine), modifyLine);

    //Execute to execute the operation
    //Must be called within QueuedTask.Run
    if (!reshapeFeatures.IsEmpty)
    {
      //Execute and ExecuteAsync will return true if the operation was successful and false if not
      var result = reshapeFeatures.Execute();
      //or use async flavor
      //await reshapeFeatures.ExecuteAsync();
    }
  });