Yes, you did it correctly.
If you decide to touch the any Virtuemart (or any Component's) PHP file. For example; in your case, it is this PHP file:
/components/com_virtuemart/views/user/tmpl/edit_vmshopper.php
then first copy-paste that PHP file to here:
/templates/flexible_lightmart/html/com_virtuemart/user/edit_vmshopper.php
and make your changes within this file.
So your change/modification won't be retrieved back to stock in case you update your Virtuemart to a newer version.
And yes, it is technically called "Template Overriding".
Regards,
Support