Maybe create a new file of the type you're working on, select-all, copy, paste and do whatever you want in the new buffer. If you "accidentally" save it, it will ask you for a file name, so you can abort it, and you'll have a very clear indicator of which is which.
I've done this occasionally when I didn't want to check the file out of source control (VERY LAZY those days) and want to try something out. Of course, if you want to diff it, you'll have to save the file, but even that isn't so bad. I'm in the habit of deleting multiple "Foo.x" files on a regular basis.
Jim