BaseFieldDefinition::setSettings

public BaseFieldDefinition::setSettings(array $settings)

  // Given these are the default settings.
  $field_definition->getSettings() === [
    'fruit' => 'apple',
    'season' => 'summer',
  ];
  // Change only the 'fruit' setting.
  $field_definition->setSettings(['fruit' => 'banana']);
  // The 'season' setting persists unchanged.
  $field_definition->getSettings() === [
    'fruit' => 'banana',
    'season' => 'summer',
  ];

public function setSettings(array $settings) {
  // Assign settings individually, in order to keep the current values
  // of settings not specified in $settings.
  foreach ($settings as $setting_name => $setting) {
    $this->getItemDefinition()->setSetting($setting_name, $setting);
  }
  return $this;
}