I seem to remember Vue boasting that you could replace objects in a scene (i.e. low poly to high poly, etc) for the render. How is that accomplished?

I'm using Vue 9 Complete, and attempting a rather intensive render, but need to 'swap out' some pieces already in place with either low poly or place holders until the final render. (Nearly impossible to work with all pieces in place at the same time)

...Insert some witty or thought provoking comment here...