public void Modify( 
   AttributedRelationshipClassDescription attributedRelationshipClassDescription
)

public void ModifyRelationshipClass(SchemaBuilder schemaBuilder, AttributedRelationshipClassDefinition attributedRelationshipClassDefinition)
{
    AttributedRelationshipClassDescription attributedRelationshipClassDescription = new AttributedRelationshipClassDescription(attributedRelationshipClassDefinition);

    // Update the relationship split policy
    attributedRelationshipClassDescription.RelationshipSplitPolicy = RelationshipSplitPolicy.UseDefault;

    // Add field in the intermediate table
    attributedRelationshipClassDescription.FieldDescriptions.Add(FieldDescription.CreateIntegerField("RelationshipStatus"));

    // Add relationship rules based on subtypes,if available
    // Assuming origin class has subtype with code 1
    attributedRelationshipClassDescription.RelationshipRuleDescriptions.Add(new RelationshipRuleDescription(1, null));

    // Enqueue modify operation
    schemaBuilder.Modify(attributedRelationshipClassDescription);

    // Execute modify DDL operation
    schemaBuilder.Build();
}

public void ModifyAnnotationLabelAndSymbols(SchemaBuilder schemaBuilder, AnnotationFeatureClassDefinition annotationFeatureClassDefinition)
{
    AnnotationFeatureClassDescription annotationFeatureClassDescription = new AnnotationFeatureClassDescription(annotationFeatureClassDefinition);
    IReadOnlyList<CIMLabelClass> labelClasses = annotationFeatureClassDescription.LabelClasses;

    // Adding a new annotation label class 
    List<CIMLabelClass> modifiedLabelClasses = new List<CIMLabelClass>(labelClasses);
    modifiedLabelClasses.Add(new CIMLabelClass()
    {
        Name = "RedSymbol",
        TextSymbol = new CIMSymbolReference
        {
            Symbol = new CIMTextSymbol()
            {
                Angle = 45,
                FontType = FontType.Type1,
                FontFamilyName = "Arial",
                FontEffects = FontEffects.Normal,
                HaloSize = 2.0,

                Symbol = new CIMPolygonSymbol { SymbolLayers = new CIMSymbolLayer[] { new CIMSolidFill { Color = CIMColor.CreateRGBColor(255, 0, 0) } }, UseRealWorldSymbolSizes = true }
            },
            MaxScale = 0,
            MinScale = 0,
            SymbolName = "TextSymbol-RED"
        },
    });

    // Adding a  new symbol
    annotationFeatureClassDescription.Symbols.Add(new CIMSymbolIdentifier()
    {
        ID = 1001,
        Name = "ID_10001",
        Symbol = new CIMTextSymbol()
        {
            Angle = 43,
            FontEffects = FontEffects.Subscript,
            FontType = FontType.TTOpenType,
            FontStyleName = "Regular",
            FontFamilyName = "Tahoma",
            TextCase = TextCase.Allcaps
        }
    });

    // Modify annotation feature class 
    AnnotationFeatureClassDescription modifiedAnnotationFeatureClassDescription = new AnnotationFeatureClassDescription(annotationFeatureClassDescription.Name, annotationFeatureClassDescription.FieldDescriptions, annotationFeatureClassDescription.ShapeDescription, annotationFeatureClassDescription.GeneralPlacementProperties, modifiedLabelClasses);

    // Enqueue modify
    schemaBuilder.Modify(modifiedAnnotationFeatureClassDescription);

    // DDL execute
    schemaBuilder.Build();

}