best practices for demo-site replication of a membership bug?
As you are in Drupal, i recommend using the drupal module masquerade which let you act as if logged in as another user.

Otherwise, with drush you could generate a one-time login for the user you want without sending an email. So from the command line, type : drush uli user-name and you will get a link that will log-in as the user user-name