What potential pitfalls should be considered when modifying the gallery_shortcode function in WordPress?

When modifying the gallery_shortcode function in WordPress, potential pitfalls to consider include compatibility issues with plugins or themes that rely on the default behavior of the function, unintended consequences such as breaking functionality in other parts of the website, and the need to properly sanitize and validate any user input to prevent security vulnerabilities.

// Example of modifying the gallery_shortcode function in WordPress
function custom_gallery_shortcode($attr) {
    // Your custom code here
}
remove_shortcode('gallery');
add_shortcode('gallery', 'custom_gallery_shortcode');