WordPress is very conducive to customization and code changes but one of the trickier things to alter are the system Widgets used in the sidebar. Some of the standard widgets included with a new install of WordPress are Archives, Calendar, Categories, Links, Meta, Pages, Recent Comments, Recent Posts, RSS and Search.
Many times you can download plugins that produce new widgets and are easier to customize but every once in a while it would be nice to just make a minor tweak on the system widgets. It’s definitely possible, but keep in mind that with each new updated version of WordPress that’s released you may be overwriting the widget file because it’s not contained in the wp-content folder with all of the other “no-change” files.
You can find the files that control all of the system widgets in WordPress in the wp-includes folder, the main file is called widgets.php but several of the systems contain their own files such as category-template.php and author-template.php. Many times you can also make changes to the way these widgets work by editing the functions.php file in WordPress, here’s a quick howto about that.
- Download the wp-includes > widgets.php file (or another file such as the category-template.php file) for your installation of WordPress
- Make a copy of the file so you can avoid breaking the system with your changes
- Use an HTML or PHP editor like Dreamweaver or Text Edit to edit bits of the file
- Upload the file to your server in the wp-includes folder and you should start seeing the changes you made instantly when you refresh any blog page that contains the widget!
WordPress structure evolves over time, for more information on this topic check out the WordPress Codex and this forum.