Customize: right-click on files "context menu"

Thanks all! With your help, I managed to get what I want - thusly.

  1. Settings -> File Types .. -> All Files -> Context Menu -> New.
  2. Change the 'New Action' text to 'Duplicate'.
  3. Put Copy DUPLICATE HERE PATTERN * AS * WHENEXISTS=rename into the text box.
  4. Press 'OK'. (One does not need to close the 'File Types') menu.

I note that at least one file manager (namely Linux's 'Nemo') has a 'duplicate' option by default. (Or rather, if I remember correctly, Nemo has a range of context-menu items that one can enable/disable via tickboxes.)