What do I have to add to a .desktop file to add it to a specific category in the menu?

Categories=Network;

Would this be enough to put a shortcut in the Network menu (using http://standards.freedesktop.org/men...egory-registry for other categories)? Because I have also found a X-Maemo-Category line in a .desktop file.
How can I update the menu without (un)installing anything or rebooting?
Thanks in advance.