Hi,

If you are referring to the diagram.undoManager.undoHistory array, it's not considered public API but you can find recorded actions as instances of AddItemCommand, RemoveItemCommand, ChangeItemCommand classes there. You could probably remove commands from it but take care that other commands do not rely on removed commands' results.

With public API you can add custom undoable actions by implementing a Command class and calling Diagram.executeCommand. You can group several actions into a single undoable action by enclosing them within Diagram.startCompositeOperation and commitCompositeOperation calls.

Regards,
Slavcho
Mindfusion