Hello,
Search is built-in. Code of the search is included in both XStore theme and XStore core plugin. Besides we use special library to display ajax search results. So, it’s not 2 lines of customization, unfortunately. PHP nad also JS files of the core plugin should be customized, so don’t think that you’ll be able to do this by yourself without problems with the next theme updates.
You may look for the third-party search plugins that have everything you need and replace the built-in search with the third-party search.
Regards