Make one site-wide change to my Wordpress eCommerce site

I currently have an eCommerce Wordpress site driven by the WooCommerce plugin. Currently, on the home page and other select pages, anywhere products are displayed, when you mouse-over the preview window, it enlarges a bit and shows additional details including the option to add the product to your cart. When clicked, it takes you to a separate page just for that one single product. I'd like to change it to... Still keep it so it enlarges a bit when moused-over, but since all of my products are videos, when clicked I would like it to pop up a small lightbox type window/box so the customer can view the video, then X out of the small window and still be at the same page and same place as before... still be able to add it to their cart, etc. I'd also like to have the image that is displayed be the video itself and not the featured image. Also, one last small request... I'd like help in backing up the site on Wordpress, then creating a child-theme so when the template is updated, I won't lose these custom changes.