How to display a customized button on a single form only?
Find the form id first.

Assume your form id is 50 than,

function &lt;module&gt;_form_alter(&amp;$form, $form_state, $form_id) {
  if (strpos($form_id, 'webform_client_form_50') === 0) {
    $form['actions']['reset'] = array(
      '#type' =&gt; 'button',
      '#value' =&gt; t('Reset'),
      '#weight' =&gt; 100,
      '#validate' =&gt; array(),
      '#attributes' =&gt; array('onclick' =&gt; 'this.form.reset(); return false;'),
    );
  }
}


OR

 if ($form_id == 'my_webform_client_form_id') {

Your code

}




Another method :- 

In Drupal 7, you can either use hook_form_alter() or hook_form__alter(), which ever you prefer. Just make sure you get the naming and parameters right. Drupal 6 only supports hook_form_alter() however.

When you create these functions, also remember that Drupal may not always pick up on them until you've flushed the cache.

function mymodule_form_webform_client_form_44_alter(&amp;$form, &amp;$form_state) {
// code here;
}


Please remember to clear your cache also and try to disable/enable your module also