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);