Can change vtbl record at runtime ?

[Виталий Фадеев via Digitalmars-d-learn]

Reason:
    Reuse component,
    bind custom callback without creating new class.
Concept example:
    class SaveFilePopup
    {
        void onSuccess() { /* default operations */ }
    }

    auto saveFile = new SaveFilePopup();
    saveFile.onSuccess = { /* New operations */ }

Delegate:
    may be... but, for speed reason, is possible to set the 
default code at compile-time ?

    class X
    {
       void delegate() onSuccess = { /* default code */ };
    }

Context:
    GUI, components, callbacks

Possible to change the vtbl record at runtime ?
Has functional for update vtbl records ?