Modifying Xubuntu application menu

One of the most disturbing features of my Xubuntu desktop is the apparent inability to modify the application menu. In particular, I had a huge settings submenu with duplicated entries: many already appeared in the system submenu.

So I edited the file /etc/xdg/menus/xfce-applications.menu and changed the section

    <Menu>
        <Name>Settings</Name>
        <Directory>xfce-settings.directory</Directory>
        <Include>
            <Category>Settings</Category>
        </Include>

        <Layout>
            <Filename>xfce-settings-manager.desktop</Filename>
            <Separator/>
            <Merge type="all"/>
        </Layout>

        <Menu>
            <Name>Screensavers</Name>
            <Directory>xfce-screensavers.directory</Directory>
            <Include>
                <Category>Screensaver</Category>
            </Include>
        </Menu>
    </Menu>

into

    <Menu>
        <Name>Settings</Name>
        <Directory>xfce-settings.directory</Directory>
        <Include>
            <Category>Settings</Category>
        </Include>
        <Exclude>
            <Or>
                <Category>System</Category>
            </Or>
        </Exclude>

        <Layout>
            <Filename>xfce-settings-manager.desktop</Filename>
            <Separator/>
            <Merge type="all"/>
        </Layout>

        <Menu>
            <Name>Screensavers</Name>
            <Directory>xfce-screensavers.directory</Directory>
            <Include>
                <Category>Screensaver</Category>
            </Include>
        </Menu>
    </Menu>

This is a simple example of what can be achieved if you (very carefully) edit the file.