*** Warning: This is only suitable for use on your own computer for test carts which are not on the public Internet. Actual live carts which are in production should abide by the forced rename so the URL to your admin is not known or easily guessed. ***
If you want to use the admin URL “admin” in Zen Cart 1.5.x, it’s a pretty simple change. Edit the file
admin/includes/init_includes/init_admin_auth.php
and insert the following line above line 12:
define('ADMIN_BLOCK_WARNING_OVERRIDE', '1');
That’s all!