code: public function changePreference($key, $preference)
  	{
  		$token = $this->oauth->getToken();
  
  		// Set parameters.
  		$parameters = array(
  			'oauth_token' => $token['key'],
  		);
  
  		// Set the API base
  		$base = 'user/preferences/' . $key;
  
  		// Build the request path.
  		$path = $this->getOption('api.url') . $base;
  
  		// Send the request.
  		$response = $this->oauth->oauthRequest($path, 'PUT', $parameters, $preference);
  
  		return $response->body;
  	}
docs: Method to change user preferences
  
  @param   string  $key         Key of the preference
  @param   string  $preference  New value for preference
  
  @return  array  The XML response
  
  @since   1.0