Recently, I finally created my own keyboard layout by edining /usr/share/X11/xkb/symbols/ru file. In the nearest future, I also will edit the corresponding xml file that provides the menu for the xfce4 keyboard layout switch plugin file deleting from it all the entries about keyboard layouts for the languages I will never use. (By the way, can anybody hint me where to find this file.)
So, my main question is How can I ensure that the already edited /usr/share/X11/xkb/symbols/ru file will not be overwritten during the next system update. Thabk you.