You can remove the duplicate function by setting up a custom menu set and not having the duplicate command in that menu set.
Here's a link for setting custom menus up in 11, I couldn't find the 12 link but it's going to be almost the same.
Hope it helps.
We Know Data
Custom menu as said Rob.
With this tecnique you can also sunstitute the default behavior with a script so, if you prefer, you could leave le shortcut but with a script prompt the user with a dialog box...
Thanks Rob. I am fairly new to this. I'll check it out.