There used to be an option for adding unlisted commands, but it seems to be gone in Unity. Does anyone know how to do that now?
one can use
mimeopen -d file to use a custom application on the cli. Afterwards it will be the default application [even from the Nautilus].
$ mimeopen -d file.txt
Please choose a default application for files of type text/plain
1) notepad (wine-extension-txt) 2) gedit (gedit) 3) GNU Emacs 23 (emacs23) 4) Other...
use application # 4
use command: nano
Opening "useful.txt" with nano (text/plain)
There are other ways you can find here