How to change custom post type slug without damage seo? [closed]

You can do this without losing SEO.

  1. Change the taxonomy slug from “watches-product” to “watches/product”


register_taxonomy('wpsc_watch_product_category', 'wpsc_watch_product', array(
'hierarchical' => true,
'query_var' => 'watch_product_category',
'rewrite' => array(
'slug' => 'watches/product'
),
'labels' => $labels,
));

  1. Install a 302 Redirect Plugin. This plugin will redirect all the traffic to new url.