Google App engine change parent of entity that is not stored
You still can't do it. You should probably delay instantiation of the MyModel object until you know its parent. Perhaps you could collect the attributes in a dictionary, then when it comes to instantiation you can do my_instance = MyModel(parent=parent_instance, **kwargs).
I know we cant change the parent of an entity that is stored , but can we change the parent of the entity that is not stored? For example i am declaring a model as 
    my_model = MyModel(parent = ParentModel1.key)
but after some checks i may have to change the parent of my_model (i have not run my_model.put() ) to ParentModel2. How can i do this ?