to replace the traffic signs, telephone booths or any other object in the streets, you can edit the objects themselves,
you can delete the instances from the road models or the building models, or you can add new objects to the road models, and then all the road instances in the city will have the changes applied.
objects instances on roads + buildings models.jpg
Oh I see what you mean... yes this is a kind of artificial intelligence that can redo a road network based on some example input model. I have one research paper where they show how they did it, and indeed that would be a very nice addition!
But before that, SceneCity must support curved roads.
I add your idea to the list of features for future releases, thank you for the feedback