The various Linux's desktops open files according to their mime type. This is a very nice feature but I also need to open them by extension (as with Windows).

For instance, I want to open every xxxxx.vnc files with a specific program when I double-click on them.
I use xfce but I don't think it differs from Gnome or KDE because all of them use the same configuration files (defaults.list and mimeapps.list).
If possible the settings are user specific, not system wide.

I've found some very poor informations about that, and all are system wide, so may be wiped out by some updates.