I'm new to Magento, but I believe that the changes we need to make would typically be made by modifying the local.xml file of the theme. My purchased theme, however, already has a very detailed local.xml. I'm hesitant to modify this because I assume it's likely to change if the theme is updated. I've tried overriding the layout under Config->Design->Themes->Layout, but when I create my own local.xml, of course the primary file is never loaded.
Is it possible for my overridden local.xml to indicate that the parent file should be ran as well? Or is there a better way to accomplish what I'm trying to do in general? I believe I could create a module that applies our layout changes, but that doesn't seem like the "right" way to do it.