Thanks for the encouragement. I have wanted to finish this addition to the project for a long time. However, it continues to get bumped back on the to do list. I think your absolutely right, the addition of a feature that would replace images based on class assignment would be a big boost to this extension's usability.
If you can't use the extension without the class based replacement feature, I completely understand. Just shoot me an email and I will make sure you're taken care of.
~ Best regards