First you want to reset the keyboard shortcuts for Duplicate to something not what we’re going to do.

Go into System Preferences, Keyboard, then to Keyboard Shortcuts. On the right, click on “All Applications” and hit the + sign button. You’ll get a window something like this:

To get the command to work, you’ve got to do it right. Type Save As with the capitalizations. You can’t type the elipses, I found; you have to use Option+semi-colon. Then in the shortcut Shift+Command+S (or whatever you want.)

So long as the program allows for Save As, it should show up in the File menu, as well!