How to change Views field settings programmatically?
UPDATED:

You can use this code snippet to change a view without views_alter:

$view = views_get_view($view_name, TRUE);
$view-&gt;display['default']-&gt;display_options['fields']['field_gallery_natural_images']['settings']['colorbox_node_style'] = 'thumbnail';
views_save_view($view);


Change default display ID if you want to use display other than the default.



If you have exported the view to code using hook_views_default_views() or the Features module, there is a hook to alter the views programmatically:

/**
 * Alter default views defined by other modules.
 *
 * This hook is called right before all default views are cached to the
 * database. It takes a keyed array of views by reference.
 *
 * Example usage to add a field to a view:
 * @code
 *   $handler =&amp; $view-&gt;display['DISPLAY_ID']-&gt;handler;
 *   // Add the user name field to the view.
 *   $handler-&gt;display-&gt;display_options['fields']['name']['id'] = 'name';
 *   $handler-&gt;display-&gt;display_options['fields']['name']['table'] = 'users';
 *   $handler-&gt;display-&gt;display_options['fields']['name']['field'] = 'name';
 *   $handler-&gt;display-&gt;display_options['fields']['name']['label'] = 'Author';
 *   $handler-&gt;display-&gt;display_options['fields']['name']['link_to_user'] = 1;
 * @endcode
 */
function hook_views_default_views_alter(&amp;$views) {
  if (isset($views['taxonomy_term'])) {
    $views['taxonomy_term']-&gt;display['default']-&gt;display_options['title'] = 'Categories';
  }
}


For example:

/**
 * Implements hook_views_default_views_alter()
 */
function MYMODULE_views_default_views_alter(&amp;$views) {
  if (isset($views['VIEW_NAME'])) {
    $views['VIEW_NAME']-&gt;display['default']-&gt;display_options['fields']['field_gallery_natural_images']['settings']['colorbox_node_style'] = 'thumbnail';
  }
}


Remember to clear the cache and do revert of the view to apply changes.