How do I replace comma with a line break in a views field?
You can use the options_form() method on your field handler to provide a setting. That setting could be a text field in which you enter separator to be used, , or &lt;br&gt; or whatever you need. Or that setting could be a select list that contained only , and &lt;br&gt; options.

Here is an example of an field handler that uses that method:

http://cgit.drupalcode.org/views/tree/modules/node/views_handler_field_node_link.inc?h=7.x-3.13

The key pieces are the options_form()

  function options_form(&amp;$form, &amp;$form_state) {
    $form['text'] = array(
      '#type' =&gt; 'textfield',
      '#title' =&gt; t('Text to display'),
      '#default_value' =&gt; $this-&gt;options['text'],
    );
    parent::options_form($form, $form_state);

    // The path is set by render_link function so don't allow to set it.
    $form['alter']['path'] = array('#access' =&gt; FALSE);
    $form['alter']['external'] = array('#access' =&gt; FALSE);
  }


and then the usage of the option

  $text = !empty($this-&gt;options['text']) ? $this-&gt;options['text'] : t('view');