title: Wordpress - Editing a plugin's filter functionality
body: <p>I was wondering if someone could help me out.</p>
  
  <p>I have a plugin called Paid Memberships Pro.</p>
  
  <p>On the signup form there are some fields i want to make required.</p>
  
  <p>I have gone through the code and found the place where it sets which fields are required and not required, as below:</p>
  
  <pre><code>//require fields
  $pmpro_required_billing_fields = array(
      "bfirstname" =&gt; $bfirstname,
      "blastname" =&gt; $blastname,
      "baddress1" =&gt; $baddress1,
      "bcity" =&gt; $bcity,
      "bstate" =&gt; $bstate,
      "bzipcode" =&gt; $bzipcode,
      "bphone" =&gt; $bphone,
      "bcountry" =&gt; $bcountry,
      "bemail" =&gt; $bemail,
      "CardType" =&gt; $CardType,
      "AccountNumber" =&gt; $AccountNumber,
      "ExpirationMonth" =&gt; $ExpirationMonth,
      "ExpirationYear" =&gt; $ExpirationYear,
      "CVV" =&gt; $CVV
  );
  $pmpro_required_billing_fields = apply_filters("pmpro_required_billing_fields", $pmpro_required_billing_fields);
  $pmpro_required_user_fields = array(
      "username" =&gt; $username,
      "password" =&gt; $password,
      "password2" =&gt; $password2,
      "bemail" =&gt; $bemail,
      "bconfirmemail" =&gt; $bconfirmemail
  );
  $pmpro_required_user_fields = apply_filters("pmpro_required_user_fields", $pmpro_required_user_fields);
  </code></pre>
  
  <p>This is found in one of the plugins core files plugins/paid-memberships-pro/preheaders/checkout.php</p>
  
  <p>I want to be able to override this, but i dont want to edit the core files, is there a way i can edit this via my themes functions.php file?</p>
  
  <p>For instance, add the bfirstname and blastname to the $pmpro_required_user_fields?</p>
  
  <p>Any help would be greatly appreciated, ive been searching how to do this but i cant really understand if its possible.</p>
  
  <p>Thanks all :)</p>