I searched everywhere in post type registration flow but didn’t found a right way (using filter or action) to do it.
All you can do either register the post type again with a different slug (I prefer) or just run those lines of code which WordPress run to build the rewrite rules in register_post_type.
I register this post type with slug book
and changed it using this trick.
I am not sure it is 100% correct (as I am rewriting rules for the same post type) but it works.
add_action('registered_post_type', 'testbook', 10, 2);
function testbook($post_type, $args) {
global $wp_rewrite;
if ($post_type == 'book') {
$args->rewrite['slug'] = 'changed_slug_book'; //write your new slug here
if ( $args->has_archive ) {
$archive_slug = $args->has_archive === true ? $args->rewrite['slug'] : $args->has_archive;
if ( $args->rewrite['with_front'] )
$archive_slug = substr( $wp_rewrite->front, 1 ) . $archive_slug;
else
$archive_slug = $wp_rewrite->root . $archive_slug;
add_rewrite_rule( "{$archive_slug}/?$", "index.php?post_type=$post_type", 'top' );
if ( $args->rewrite['feeds'] && $wp_rewrite->feeds ) {
$feeds="(" . trim( implode( '|', $wp_rewrite->feeds ) ) . ')';
add_rewrite_rule( "{$archive_slug}/feed/$feeds/?$", "index.php?post_type=$post_type" . '&feed=$matches[1]', 'top' );
add_rewrite_rule( "{$archive_slug}/$feeds/?$", "index.php?post_type=$post_type" . '&feed=$matches[1]', 'top' );
}
if ( $args->rewrite['pages'] )
add_rewrite_rule( "{$archive_slug}/{$wp_rewrite->pagination_base}/([0-9]{1,})/?$", "index.php?post_type=$post_type" . '&paged=$matches[1]', 'top' );
}
$permastruct_args = $args->rewrite;
$permastruct_args['feed'] = $permastruct_args['feeds'];
add_permastruct( $post_type, "{$args->rewrite['slug']}/%$post_type%", $permastruct_args );
}
}