As the object returned by poser.Scene() is a wrapped native object, it doesn't allow you to add new members just by assignment, and there is no dict attribute to manipulate.

Even if the implementation allowed you to modify a scene object, you'd have to make the same modification each time you called poser.Scene() as the wrapper object returned is different for each call.

Basically any object with a dict attribute can be extended, but you have to be careful of wrappers as their lifetime may not be the same as the underlying native object.