Changing the /category/ label in the URL. Eg http://mywebsite.com/downloads/category/ebooks/ to http://mywebsite.com/downloads/cat/ebooks/. Replace "the-new-category-label" with what you'd like.

gistfile1.php

<?php

function my_child_theme_edd_download_category_args( $category_labels ) {
	$slug = defined( 'EDD_SLUG' ) ? EDD_SLUG : 'downloads';
	
	// modify the "the-new-category-label" below to your liking
	$category_labels['rewrite'] = array('slug' => $slug . '/the-new-category-label', 'with_front' => false, 'hierarchical' => true );

	return $category_labels;
}
add_filter( 'edd_download_category_args', 'my_child_theme_edd_download_category_args' );