Reset the slugs on a particular post type to use the default sanitized slugs. To use, add the following code into your theme's functions.php file, ensure that the desired post type is set when calling `wp20140226_reset_slugs('post');` Then navigate to `wp-admin/options-permalink.php` to activate query to reset slugs. Depending on how many posts …

wp20140226_reset_slugs.php

<?php


/**
 * Reset the slugs on a particular post type to use the default sanitized slugs
 * @param  string  $post_type         filter by post type
 * @param  int $offset                set the paginated post to start
 * @param  boolean $force_guid_update * WARNING * never enable this
 *
 * @example add the following code into your theme's functions.php file, ensure
 * that the desired post type is set when calling wp20140226_reset_slugs('post');
 * Then navigate to wp-admin/options-permalink.php to activate query to reset slugs.
 * Depending on how many posts need to be updated this method may take quite 
 * some time, on a shared host there may be a need to set the $offset argument
 * to limit the amount of time the script runs and use multiple calls by adjusting
 * the offset to progress through the entire record set.
 * 
 */
function wp20140226_reset_slugs( $post_type = null, $offset = 0, $force_guid_update = false ){
	global $pagenow, $wpdb;

    if ( $pagenow != 'options-permalink.php' || empty($post_type) )
		return;

	$get_post_args = array(
		'post_type' => $post_type, 
		'post_status' => 'any'
		);

	if( $offset == 0 ){
		$get_post_args['posts_per_page'] = -1;
	} else {
		$get_post_args['offset'] = $offset;
	}

	$posts_to_fix = new WP_Query( $get_post_args );

	foreach( $posts_to_fix->posts as $post_to_fix ){
		$wpdb->update( 
			$wpdb->posts, 
			array( 'post_name' => sanitize_title( $post_to_fix->post_title ) ), 
			array( 'ID' => $post_to_fix->ID ), 
			array( '%s' ), 
			array( '%d' ) 
		);
	}

	// you should really leave this alone (do not set to true unless you need to)
	//http://codex.wordpress.org/Changing_The_Site_URL#Important_GUID_Note
	if( $force_guid_update ){
		$siteurl = trailingslashit( get_option('siteurl') );
		$wpdb->query( "UPDATE {$wpdb->posts} SET guid = CONCAT( '{$siteurl}?p=', ID ) WHERE post_type = {$post_type} OR post_type = 'revision';" );
	}
	
	add_action('admin_notices', 'wp20140226_reset_slugs_admin_notice');

}

/**
 * notify the user when the reset slug queries are run
 */
function wp20140226_reset_slugs_admin_notice(){
	?>
    <div class="updated">
        <p><?php _e('You have successfully run the reset slugs function, please disable or suffer impact when in the admin.'); ?></p>
    </div>
    <?php
}

wp20140226_reset_slugs('post'); // change this to be your custom post type