Right, so I went to my town hall today to change the exterior of my town hall but Isabelle came up with the "this project cannot be destroyed" dialogue. Does this mean that once I've chosen the style I can never go back? I like the default but I want to see what my town looks like with the other styles too.
That just means you can't "destroy" it to get the original exterior back. You have to pay for the full renovation to change it back to the original.