Resize field

demo_field_resize.install

use Drupal\field\Entity\FieldStorageConfig;

/**
 * Resize field.
 */
function demo_field_resize_update_8001() {
  $field_name = 'field_to_resize';
  $entity_type = 'node';
  $database = \Drupal::database();
  $database->query("ALTER TABLE node__" . $field_name . " MODIFY " . $field_name . "_value VARCHAR(200)");
  $database->query("ALTER TABLE node_revision__" . $field_name . " MODIFY " . $field_name . "_value VARCHAR(200)");

  $storage_key = 'node.field_schema_data.' . $field_name;
  $storage_schema = \Drupal::keyValue('entity.storage_schema.sql');
  $field_schema = $storage_schema->get($storage_key);
  $field_schema['node__' . $field_name]['fields'][$field_name . '_value']['length'] = 200;
  $field_schema['node_revision__' . $field_name]['fields'][$field_name . '_value']['length'] = 200;
  $storage_schema->set($storage_key, $field_schema);

  $config = \Drupal::configFactory()
    ->getEditable('field.storage.node.' . $field_name);
  $config->set('settings.max_length', 200);
  $config->save(TRUE);

  FieldStorageConfig::loadByName($entity_type, $field_name)->save();
}