Drupal - Resize field with already existing data

drupal-resize-field.php

<?php

/**
 * Increase the length of "field_one" to 512 characters.
 */
function trimis_cordis_update_9001() {
  // Resize field DB column
  $database = \Drupal::database();
  $database->query("ALTER TABLE node__field_one MODIFY field_one_value VARCHAR(512)");
  $database->query("ALTER TABLE node_revision__field_one MODIFY field_one_value VARCHAR(512)");

  // Update field schema
  $storage_key = 'node.field_schema_data.field_one';
  $storage_schema = \Drupal::keyValue('entity.storage_schema.sql');
  $field_schema = $storage_schema->get($storage_key);
  $field_schema['node__field_one']['fields']['field_one_value']['length'] = 512;
  $field_schema['node_revision__field_one']['fields']['field_one_value']['length'] = 512;
  $storage_schema->set($storage_key, $field_schema);

  // Update field configuration
  $config = \Drupal::configFactory()
    ->getEditable('field.storage.node.field_one');
  $config->set('settings.max_length', 512);
  $config->save(TRUE);
}