I went into Preferences => Save to disk and replaced my current template with {title} and clicked on Apply. Restarted calibre, went back to the template and it was {title} so it appears to work here.
I've attached some images. The first one is my original setup where you can see the Apply button is greyed out. The second is after I edited the template to {title} where you will notice the Apply button is now available. After I hit apply and restarted calibre, I re-opened the preference and it still shows {title} and the Apply button is greyed out.
Edit: please note that this is for the Save to Disk function. If you want to modify the structure of the calibre library directories, forget it.
See these posts:
Want to change folder structure or file names in the Calibre library? and
Changing the Calibre File Structure.