public abstract class CIMGeneralPlacementProperties : CIMObject, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

public void CreateStandAloneAnnotationFeatureClass(Geodatabase geodatabase, SpatialReference spatialReference)
{
  // Creating a Cities annotation feature class
  // with following user defined fields
  // Name 
  // GlobalID

  // Annotation feature class name
  string annotationFeatureClassName = "CitiesAnnotation";

  // Create user defined attribute fields for annotation feature class 
  FieldDescription globalIDFieldDescription = FieldDescription.CreateGlobalIDField();
  FieldDescription nameFieldDescription = FieldDescription.CreateStringField("Name", 255);

  // Create a list of all field descriptions
  List<FieldDescription> fieldDescriptions = new List<FieldDescription> { globalIDFieldDescription, nameFieldDescription };

  // Create a ShapeDescription object
  ShapeDescription shapeDescription = new ShapeDescription(GeometryType.Polygon, spatialReference);

  // Create general placement properties for Maplex engine 
  CIMMaplexGeneralPlacementProperties generalPlacementProperties =
    new CIMMaplexGeneralPlacementProperties
    {
      AllowBorderOverlap = true,
      PlacementQuality = MaplexQualityType.High,
      DrawUnplacedLabels = true,
      InvertedLabelTolerance = 1.0,
      RotateLabelWithDisplay = true,
      UnplacedLabelColor = new CIMRGBColor
      {
        R = 0,
        G = 255,
        B = 0,
        Alpha = 0.5f // Green
      }
    };

  // Create general placement properties for Standard engine

  //CIMStandardGeneralPlacementProperties generalPlacementProperties =
  //  new CIMStandardGeneralPlacementProperties
  //  {
  //    DrawUnplacedLabels = true,
  //    InvertedLabelTolerance = 3.0,
  //    RotateLabelWithDisplay = true,
  //    UnplacedLabelColor = new CIMRGBColor
  //    {
  //      R = 255, G = 0, B = 0, Alpha = 0.5f // Red
  //    } 
  //   };


  // Create annotation  label classes
  // Green label
  CIMLabelClass greenLabelClass = new CIMLabelClass
  {
    Name = "Green",
    ExpressionTitle = "Expression-Green",
    ExpressionEngine = LabelExpressionEngine.Arcade,
    Expression = "$feature.OBJECTID",
    ID = 1,
    Priority = 0,
    Visibility = true,
    TextSymbol = new CIMSymbolReference
    {
      Symbol = new CIMTextSymbol()
      {
        Angle = 45,
        FontType = FontType.Type1,
        FontFamilyName = "Tahoma",
        FontEffects = FontEffects.Normal,
        HaloSize = 2.0,

        Symbol = new CIMPolygonSymbol
        {
          SymbolLayers = new CIMSymbolLayer[]
          {
            new CIMSolidFill
            {
              Color = CIMColor.CreateRGBColor(0, 255, 0)
            }
          },
          UseRealWorldSymbolSizes = true
        }
      },
      MaxScale = 0,
      MinScale = 0,
      SymbolName = "TextSymbol-Green"
    },
    StandardLabelPlacementProperties = new CIMStandardLabelPlacementProperties
    {
      AllowOverlappingLabels = true,
      LineOffset = 1.0
    },
    MaplexLabelPlacementProperties = new CIMMaplexLabelPlacementProperties
    {
      AlignLabelToLineDirection = true,
      AvoidPolygonHoles = true
    }
  };

  // Blue label
  CIMLabelClass blueLabelClass = new CIMLabelClass
  {
    Name = "Blue",
    ExpressionTitle = "Expression-Blue",
    ExpressionEngine = LabelExpressionEngine.Arcade,
    Expression = "$feature.OBJECTID",
    ID = 2,
    Priority = 0,
    Visibility = true,
    TextSymbol = new CIMSymbolReference
    {
      Symbol = new CIMTextSymbol()
      {
        Angle = 45,
        FontType = FontType.Type1,
        FontFamilyName = "Consolas",
        FontEffects = FontEffects.Normal,
        HaloSize = 2.0,

        Symbol = new CIMPolygonSymbol
        {
          SymbolLayers = new CIMSymbolLayer[]
          {
            new CIMSolidFill
            {
              Color = CIMColor.CreateRGBColor(0, 0, 255)
            }
          },
          UseRealWorldSymbolSizes = true
        }
      },
      MaxScale = 0,
      MinScale = 0,
      SymbolName = "TextSymbol-Blue"
    },
    StandardLabelPlacementProperties = new CIMStandardLabelPlacementProperties
    {
      AllowOverlappingLabels = true,
      LineOffset = 1.0
    },
    MaplexLabelPlacementProperties = new CIMMaplexLabelPlacementProperties
    {
      AlignLabelToLineDirection = true,
      AvoidPolygonHoles = true
    }
  };

  // Create a list of labels
  List<CIMLabelClass> labelClasses = new List<CIMLabelClass> { greenLabelClass, blueLabelClass };

  // Create an annotation feature class description object to describe the feature class to create
  AnnotationFeatureClassDescription annotationFeatureClassDescription =
    new AnnotationFeatureClassDescription(annotationFeatureClassName, fieldDescriptions, shapeDescription,
      generalPlacementProperties, labelClasses)
    {
      IsAutoCreate = true,
      IsSymbolIDRequired = false,
      IsUpdatedOnShapeChange = true
    };

  // Create a SchemaBuilder object
  SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

  // Add the creation of the Cities annotation feature class to the list of DDL tasks
  schemaBuilder.Create(annotationFeatureClassDescription);

  // Execute the DDL
  bool success = schemaBuilder.Build();

  // Inspect error messages
  if (!success)
  {
    IReadOnlyList<string> errorMessages = schemaBuilder.ErrorMessages;
    //etc.
  }
}

//Note: call within QueuedTask.Run()

//Get the active map's definition - CIMMap.
var cimMap = MapView.Active.Map.GetDefinition();
//Get the labeling engine from the map definition
CIMGeneralPlacementProperties labelEngine = cimMap.GeneralPlacementProperties;

//Note: call within QueuedTask.Run()

//Get the active map's definition - CIMMap.
var cimMap = MapView.Active.Map.GetDefinition();
//Get the labeling engine from the map definition
var cimGeneralPlacement = cimMap.GeneralPlacementProperties;

if (cimGeneralPlacement is CIMMaplexGeneralPlacementProperties)
{
  //Current labeling engine is Maplex labeling engine
  //Create a new standard label engine properties
  var cimStandardPlacementProperties = new CIMStandardGeneralPlacementProperties();
  //Set the CIMMap's GeneralPlacementProperties to the new label engine
  cimMap.GeneralPlacementProperties = cimStandardPlacementProperties;
}
else
{
  //Current labeling engine is Standard labeling engine
  //Create a new Maplex label engine properties
  var cimMaplexGeneralPlacementProperties = new CIMMaplexGeneralPlacementProperties();
  //Set the CIMMap's GeneralPlacementProperties to the new label engine
  cimMap.GeneralPlacementProperties = cimMaplexGeneralPlacementProperties;
}
//Set the map's definition
MapView.Active.Map.SetDefinition(cimMap);