Warning: this is a hidden undocumented and unsupported feature and is not intended for general use. Proceed with caution unless you are working with Support, Services, or Engineering.
Warning: modification of hidden properties is intended for guided configuration change or troubleshooting. They are not expected to be left in a modified state for general operation.
Navigate to the blind URL https ://<servername>/shepherd_config.php
In the dropdown menu, select ShowHiddenCustomRules. Change the value to 'true' and save the change.

From there, navigate to the Custom Rules page to view and edit advanced Custom Rules.
To revert, set the Property Value back to 'false' and save the change.