Overriding an entity add/edit form through alterroute
Alternatively, you can use hook_entity_type_alter() to override the default form handler classes. It would be something like:

/**
 * Implements hook_entity_type_alter().
 */
function mymod_entity_type_alter(array &amp;$entity_types){
  $entity_types['commerce_product']-&gt;setHandlerClass('form', array(
    'edit' =&gt; 'Drupal\mymod\Form\EventForm'
  ));
}