In this article, I’m going to be covering what I believe to be a very effective way of modifying the layout of any Magento theme.
For several of the first Magento themes I built, I copied the layout files from the default or blank theme into the custom theme layout folder. I would then modify the layout files directly, editing or commenting out content in files like: catalog.xml, page.xml, checkout.xml, etc… I never liked editing these files directly, as I knew that when it came time to upgrade to a newer version of Magento that had upgraded the layout files, I’d have to merge the changes into the new layout files.
One day, I was digging through the Magento code relating to layout files and discovered a bit of code that made me realize that it was possible to just place a local.xml file in my custom theme’s layout folder and have it loaded automatically by Magento. (this code is on line 283 in /app/code/core/Mage/Core/Model/Layout/Update.php in the fetchFileLayoutUpdates() method).
Due to Magento’s brilliant tags, it’s possible to do just about anything you want without having to edit any of the default layout files.