v2.2.1 of EMP has been validated with Zen Cart 1.5.3 through 1.5.5a and only affects the built-in Zen Cart Customers->Customers processing (using the ZC 1.5.5a version of those customers.php files).
v2.2.1 of EMP has been validated with Zen Cart 1.5.3 through 1.5.5a and only affects the built-in Zen Cart Customers->Customers processing (using the ZC 1.5.5a version of those customers.php files).
Since you're running on Zen Cart 1.5.4, EMP will require modification to the module (/YOUR_ADMIN/customers.php) that handles the processing when you click your admin menu's Customers->Customers link.
No changes will be made to the customer information that you have already entered.