wp-rewrite.php

<?php

// rewrite rules
add_action('init', function () {
    // show all pages under '/p/{pagename}'
    global $wp_rewrite;
    $wp_rewrite->page_structure = $wp_rewrite->root . 'p/%pagename%/';
    // show all review pages under '/reviews/{pagename}'
    add_rewrite_tag('%is_review%', '([^&]+)');
    add_rewrite_rule('reviews/([^/]*)/?', 'index.php?pagename=$matches[1]&is_review=true', 'top');
    flush_rewrite_rules();
}, 10, 0);

// handle redirection
add_action( 'template_redirect', function () {
	global $post, $wp_query;
	if (empty($wp_query->query_vars['is_review'])) return;
	if (!is_page_template('page-review.php')) {
		show404();
	}
}, 1);

// update links in the backend for the pages that use a specific template
add_filter('page_link', function ($link, $post_id, $sample) {
	if (get_page_template_slug($post_id) == 'page-review.php') {
		return str_replace('/p/', '/reviews/', $link);
	}
	return $link;
}, 10, 3);

// execute 404 
function show404() {
	global $wp_query;
	$wp_query->set_404();
	status_header(404);
	get_template_part(404); 
	exit();
}