Drupal 7 override image styles programmatically

/**
 * Implements hook_image_styles_alter().
 */
function mymodule_image_styles_alter(&$styles) {
  // Check that we only affect a default style.
  if (isset($styles['thumbnail_large']) && isset($styles['thumbnail_large']['storage'])) {

    if ($styles['thumbnail_large']['storage'] == IMAGE_STORAGE_DEFAULT) {

      $styles['thumbnail_large'] = array(
        'name' => 'thumbnail_large',
        'effects' => array(
          1 => array(
            'label' => 'Javascript crop',
            'help' => 'Create a crop with a javascript toolbox.',
            'effect callback' => 'imagecrop_effect',
            'form callback' => 'imagecrop_effect_form',
            'summary theme' => 'imagecrop_effect_summary',
            'module' => 'imagecrop',
            'name' => 'imagecrop_javascript',
            'data' => array(
              'width' => '620',
              'height' => '350',
              'xoffset' => 'center',
              'yoffset' => 'center',
              'resizable' => 1,
              'downscaling' => 1,
              'aspect_ratio' => 'CROP',
              'disable_if_no_data' => 1,
            ),
            'weight' => '1',
          ),
          2 => array(
            'label' => 'Scale and crop',
            'help' => 'Scale and crop will maintain the aspect-ratio of the original image, then crop the larger dimension. This is most useful for creating perfectly square thumbnails without stretching the image.',
            'effect callback' => 'image_scale_and_crop_effect',
            'dimensions callback' => 'image_resize_dimensions',
            'form callback' => 'image_resize_form',
            'summary theme' => 'image_resize_summary',
            'module' => 'image',
            'name' => 'image_scale_and_crop',
            'data' => array(
              'width' => '620',
              'height' => '350',
            ),
            'weight' => '2',
          ),
        ),
        'label' => 'thumbnail_large',
      );
    }
  }
}

Add / Change arguments in a view programmatically (Drupal 6)

function hook_views_pre_view(&$view, &$display_id, &$args) {
    if ($view->name == 'your_view_name') {
         $view->set_arguments(array(arg1,arg2,arg3));
    }
}