At present I’m using this permalink structure
/%category%/%postname%/. There are some existing post type. I want to change permalink for image post type to
image/%post_id%/, and don’t want to affect other post type and their permalinks.
This will be done when you register_post_type :
$args = array( 'rewrite' => array( 'slug' => 'book' ), ); register_post_type( 'book', $args );
IMPORTANT ! Remember to go to wp-admin options > permalink and click SAVE on that page for the changes to take effect.
I would give the Custom Post Type Permalinks plugin a try (it sounds like it will allow you to do exactly what you want).
Alternatively you could probably manually edit your rewrite rules (in .htaccess), however re-saving your permalink settings would probably reset your rules each time.
Hope that helps, have fun!