private.xml

<?xml version="1.0"?>
<!-- http://blog.glidenote.com/blog/2014/08/06/custom-keybind-for-slack/ -->
<root>
    <appdef>
        <appname>SLACK</appname>
        <equal>com.tinyspeck.slackmacgap</equal>
    </appdef>
    <item>
        <name>Slack keyboard shortcut like LimeChat</name>
        <identifier>private.app_slack_like_limechat</identifier>
        <only>SLACK</only>
        <autogen>
            __KeyToKey__
            KeyCode::CURSOR_DOWN, ModifierFlag::COMMAND_L,
            KeyCode::CURSOR_DOWN, ModifierFlag::OPTION_L
        </autogen>
        <autogen>
            __KeyToKey__
            KeyCode::CURSOR_UP, ModifierFlag::COMMAND_L,
            KeyCode::CURSOR_UP, ModifierFlag::OPTION_L
        </autogen>
        <autogen>
            __KeyToKey__
            KeyCode::SPACE, ModifierFlag::OPTION_L,
            KeyCode::CURSOR_DOWN, ModifierFlag::OPTION_L,
            ModifierFlag::SHIFT_L
        </autogen>

        <autogen>
            __KeyToKey__
            KeyCode::CURSOR_DOWN, ModifierFlag::COMMAND_L,
            KeyCode::CURSOR_DOWN, ModifierFlag::OPTION_L
        </autogen>
    </item>
</root>