Alphabetize Category Posts Using ‘pre_get_posts’ Action

Occasionally you want to have a different sort order in some of the category archives, for example, you want to output the posts of a specific category in alphabetical order.
Instead of having to create a category template for each of those categories and to add a custom query to change the query parameters, WordPress providdes the ‘pre_get_posts’ action where you can add a corresponding function:

function category_archive_sort_alphabetical( $query ) {
    if ( is_admin() || ! $query->is_main_query() )
        return;

    if ( is_category( array( 'Category One', 'category-two', 'Another Cat' ) ) ) {
		$query->set( 'orderby', 'title' );
		$query->set( 'order', 'ASC' );
        return;
    }
}
add_action( 'pre_get_posts', 'category_archive_sort_alphabetical', 1 );

resources:
http://codex.wordpress.org/Plugin_API/Action_Reference/pre_get_posts
http://codex.wordpress.org/Function_Reference/is_category