Source

This is all based on http://rlog.rgtti.com/2014/05/01/how-to-modify-a-keyboard-layout-in-linux

I made a change to /usr/share/X11/xkb/symbols/be.

The following was added:

// Coder layout
partial alphanumeric_keys
xkb_symbols "coder" {
    include "be(basic)"
    name[Group1]="Belgian (Coder)";

    key <BKSL>	{ [        grave, mu,   sterling,      dead_breve ]	};
    key <AE09>	{ [    braceleft,  9,   ccedilla,       plusminus ]	};
    key <AE10>	{ [   braceright,  0,     agrave,          degree ]	};

};

Then changes were made to 4 files in /usr/share/X11/xkb/rules. The files are evdev.lst, evdev.xml, base.lst, base.xml.

.lst-files

  coder     be: Belgian (Coder)

.xml-files

        <variant>
          <configItem>
            <name>coder</name>
            <description>Belgian (Coder)</description>
          </configItem>
        </variant>