Yeah, go to Misc & Uninstall in Karabiner, click 'open private.xml', rightclick the file and open in textedit, and replace the contents with this. This will give you a new rule which you can toggle.
<?xml version="1.0"?>
<root>
<item>
<name>Swap backslash and backtick</name>
<identifier>private.swap_backslash_and_backtick</identifier>
<autogen>__KeyToKey__ KeyCode::BACKQUOTE, KeyCode::BACKSLASH</autogen>
<autogen>__KeyToKey__ KeyCode::BACKSLASH, KeyCode::BACKQUOTE</autogen>
</item>
</root>