Based on Master Password v1.0 by Acheron for OSC 2.2 All credit to original authors
I needed a simple Master Password modification that actually works.
This simple mod will add a master password to your site which will allow you to login to any customer's account.
Possible uses include:
(a) completing checkout if a customer did not return to your site from the payment processor,
(b) troubleshoot a customer's account,
(c) manually enter orders for existing customers,
(d) Reset the customers password for them
The master password can be set and changed in the Admin CP: Administration --> Configuration --> My Store