title: disable single variation if user is in specific group
body: <p>i have a product with 6 variations of Membership (MEMBER, SPECIALMEMBER, NOMEMBER...)
  it is possible to enable or disable purchase of this whole product (all variations), if the logged in user is in member group &quot;specialmembers&quot;.</p>
  <pre><code>if ( user_can( $current_user, &quot;specialmember&quot; )) {
       return true;
       }
  else {
       return true;
       }
  </code></pre>
  <p>How is it possible to disable just one single variation (MEMBER) für this user group?</p>
  <p>Thank you very much for helping a beginner!</p>