Cannot update Gist when the project has been saved locally

1. I publish project as Gist.
2. Then do File > Save to a local folder.
3. Make changes to the project.

Now i want to update the Gist, but cannot. When I paste Gist URL to the Gist URL input field, I can do only:
* "Load Fiddle", then replace each file copy&paste, then update the Fiddle. It's tedious.
* Publish as a new Gist and delete the old one. This is inconvenient when I have shared the Gist URL with someone already.