// Init API
Library api = Library.GetInstance();
api.Init();

// Set library connection.
api.AddLibraryConnection(@"c:\Users\test\Documents\Harness proD 2024\Connections\Demo.hxcn");
BaseLibraryConnection connection = api.CurrentLibrary.Connection;
api.ConnectToLibrary(connection);

// Select a part.
BaseConstructionItem part = api.CurrentLibrary.GetAllLibraryParts().OfType<CountableLibraryPart>().FirstOrDefault(p => p.PartNumber == "c-0206430");
part.Open();

// Select an accessory.
AccessoryInfo accessoryToUpdate = part.Accessories[1];
					
// Copy properties and update them.
CountableLibraryPart accessoryPart = accessoryToUpdate.Part as CountableLibraryPart;
BooleanProperty isMandatory = !accessoryToUpdate.Mandatory;
IntegerProperty quantity = accessoryToUpdate.Quantity + 3;
TextProperty accessoryPlacement = accessoryToUpdate.AccessoryPlacement;
					
// Create a new accessory.
AccessoryInfo newAccessory = AccessoryInfo.CreateInstance(accessoryPart, isMandatory, quantity, accessoryPlacement);
					
// Update it in collection.
part.Accessories[1] = newAccessory;
					
// Save changes and close.
part.Save();
part.Close();

api.Close();