[Plugin: Formidable] Creating custom shortcodes

Is is possible to create a a shortcode to check a value?

I’ve seen this <td class=”[if id equals=”20″]red[/if id]”>[id]</td>

But would it be possible to check if the value is greater or less than?

ie <td class=”[if id greater>”20″]red[/if id]”>[id]</td>
or <td class=”[if id less<“20″]blue[/if id]”>[id]</td>

I can create basic short codes for adding atributes to, say, image src, width, height etc but I’m lost with how to implement this.

Any help appreciated,
Sam