This is a new answer to an old question. It's somewhat similar to the existing answers, but I think different enough and easy enough to be of value.
1) Save the existing project/solution to version control just as good practice.
2) When re-scaffolding, use a different controller name which will create a controller class and it's 5 attendant views, but it won't overwrite anything that exists, preserving all your existing work.
3) Extract the appropriate methods from the re-scaffolded controller. Bindings for create/edit will likely change when the model changes, so capture those. Then delete the re-scaffolded controller.
4) That leaves the views in place to copy and paste the appropriate UI code for any new or redefined model properties. Once all the code needed has been copied, simply delete the re-scaffolded views.
It was a great question because we often have to change a model, and it's nice to have all the basic UI stuff automatically created for us.