public List<RelationshipRuleDescription> RelationshipRuleDescriptions {get;}

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();
}