oxoxTali on "Is it possible to edit HTML in a child theme?"

I've been using a child theme to edit CSS on my blog but I'd like to edit the HTML as well.

Specifically, what I want to do is replace the stock image of a computer monitor with my own image, and I want the image to change each time the page is refreshed (set it to choose from 5 different images or so).

I hope I'm explaining this clearly. Here is a link to my blog:

http://oxoxtali.com