Karabiner for Slack (~/Library/Application\ Support/Karabiner)

private.xml

<?xml version="1.0"?>
<root>
    <appdef>
        <appname>SLACK</appname>
        <equal>com.tinyspeck.slackmacgap</equal>
    </appdef>
    <item>
        <name>For Slack CTRL+N=move next channel, CTRL+P=move previous channel, ALT+A=move unread channel</name>
        <identifier>private.app_slack_move_channel_with_ctrln_ctrlp</identifier>
        <only>SLACK</only>
        <autogen>
            __KeyToKey__
            KeyCode::N, ModifierFlag::CONTROL_L,
            KeyCode::CURSOR_DOWN, ModifierFlag::OPTION_L
        </autogen>
        <autogen>
            __KeyToKey__
            KeyCode::P, ModifierFlag::CONTROL_L,
            KeyCode::CURSOR_UP, ModifierFlag::OPTION_L
        </autogen>
        <autogen>
            __KeyToKey__
            KeyCode::A, ModifierFlag::OPTION_L,
            KeyCode::CURSOR_DOWN, ModifierFlag::OPTION_L, ModifierFlag::SHIFT_L
        </autogen>
    </item>
    <item>
        <name>For Slack Fn+Return=create snippet, CTRL+Return=post message, Return=new line</name>
        <identifier>private.app_slack_swap_enter_with_command_r</identifier>
        <only>SLACK</only>
        <autogen>
            __KeyToKey__
            KeyCode::RETURN, ModifierFlag::FN,
            KeyCode::RETURN, ModifierFlag::COMMAND_R
        </autogen>
        <autogen>
            __KeyToKey__
            KeyCode::RETURN, ModifierFlag::COMMAND_R,
            KeyCode::RETURN
        </autogen>
        <autogen>
            __KeyToKey__
            KeyCode::RETURN,
            KeyCode::RETURN, ModifierFlag::OPTION_L
        </autogen>
    </item>
</root>