Arrow [Q] Help on custom theme?

So I'm pretty new to root so any help would be appreciated. I am running carbon rom on my nexus 4. I've recently been playing around with themes and mods and not sure if this is where I would ask this question or not. I installed a custom theme (root* not a launcher) but I don't like the lock screen. Tried zip themer but nothing sticks. After reading more about it, from what I understand, and correct me if I am wrong, is the reason it won't work is because a theme redirect the request for that image (default lock screen image) to its image. And the mods I am using through zip themer change the default images not the themes images. So my question is, how do I modify the themes lock screen image to what I want?