Here’s a quick snippet to set staging mode on WooCommerce Subscriptions:

add_filter( 'woocommerce_subscriptions_is_duplicate_site', '__return_true' );

What does this do?

This will set WooCommerce Subscriptions in staging mode. Basically, switching all Subscription renewals to Manual renewals and disabling all Subscription emails.

Usage:

You can either place the snippet on your child themes functions.php or use a plugin like Code Snippets to add the snippet.