[gentoo-user] preventing keyboard layout files from being overritten during system upgrades

[gevisz]

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.