E-mail is always shows and always required. How to hide it?

First of all: I'm using CS-cart pro 3.0.6 and template 'basic' as it comes with the installation.

I'm searching for a way to disable the ability for a customer to change his/her e-mail address after registration because we only allow customers depending on a payed subscription.

Whenever I go to 'profile fields' in the backend the e-mail address however is a radiobutton instead of a check button and when editing this profile field the checkboxes to 'show' and 'require' the e-mail are disabled.

I already altered 'manage.tpl' and 'update.tpl' in the directory 'skins[basic]\admin\views\profile_fields' and it's corresponding 'var\skin_repository' directory.

But somehow the buttons still stay disabled, even after clearing cache on the browser of course.

How can I resolve this?

You might have forgotten to flush cache. Add &cc and refresh.