Remap LShift+Space to underscore (_) on OS X in Karabiner's private.xml

private.xml

<?xml version="1.0"?>
<root>
    <item>
        <name>Remap Shift_L-Space to Underscore (_)</name>
        <appendix>Easier to type this way.</appendix>
     
        <identifier>shift_space_to_underscore</identifier>
     
        <autogen>
            --KeyToKey--
            KeyCode::SPACE,
            ModifierFlag::SHIFT_L,
     
            KeyCode::MINUS,
            ModifierFlag::SHIFT_L
        </autogen>
    </item>
</root>