title: Adding a custom field to BACS account fields without overriding core files
body: <p>I have this situation - I made a changes in one of the woocommerce email templates, but I`m sure - these changes will be lost after next woocommerce update. </p>
  
  <p>As I know, I should use theme functions to bypass this problem.</p>
  
  <p>This is the code before changes:</p>
  
  <pre><code>echo '&lt;ul class="wc-bacs-bank-details order_details bacs_details"&gt;' . PHP_EOL;
  
                  // BACS account fields shown on the thanks page and in emails
                  $account_fields = apply_filters( 'woocommerce_bacs_account_fields', array(
                      'account_number'=&gt; array(
                          'label' =&gt; __( 'Account Number', 'woocommerce' ),
                          'value' =&gt; $bacs_account-&gt;account_number
                      ),
                      'sort_code'     =&gt; array(
                          'label' =&gt; $sortcode,
                          'value' =&gt; $bacs_account-&gt;sort_code
                      ),
                      'iban'          =&gt; array(
                          'label' =&gt; __( 'IBAN', 'woocommerce' ),
                          'value' =&gt; $bacs_account-&gt;iban
                      ),
                      'bic'           =&gt; array(
                          'label' =&gt; __( 'BIC', 'woocommerce' ),
                          'value' =&gt; $bacs_account-&gt;bic
                      )
  
                  ), $order_id );
  
                  foreach ( $account_fields as $field_key =&gt; $field ) {
                      if ( ! empty( $field['value'] ) ) {
                          echo '&lt;li class="' . esc_attr( $field_key ) . '"&gt;' . esc_attr( $field['label'] ) . ': &lt;strong&gt;' . wptexturize( $field['value'] ) . '&lt;/strong&gt;&lt;/li&gt;' . PHP_EOL;
                      }
                  }
  
                  echo '&lt;/ul&gt;';
  </code></pre>
  
  <p>Here is the custom account field code that I want to insert:                </p>
  
  <pre><code>'merkis' =&gt; array(
      'label' =&gt; $merkis,
      'value' =&gt; $pasutijums
  )
  </code></pre>
  
  <p>How can I insert my custom code without overriding that core file? </p>
  
  <p>Thanks</p>