Here’s how to null North theme (and Werkstatt theme by the same company…)

in the file north-wp/inc/admin/welcome/fuelthemes.php around line 85 replace this:

self::$thb_product_key = get_option("thb_".self::$thb_theme_slug."_key");
self::$thb_product_key_expired = get_option("thb_".self::$thb_theme_slug."_key_expired");

with this:

self::$thb_product_key = "whatever_licensekey_you_want_to_display_here";
self::$thb_product_key_expired = 0;

Now you can install plugins and demo content.

Demo installation does not install the required plugins… you must install the plugins separately from the demo content.