I've successfully set several overrides in civicrm.setting.php according to https://docs.civicrm.org/sysadmin/en/latest/customize/settings/. However, both Recatpcha and the USPS Address standardization tool break the site. Setting USPS provider line does work.
I'm doing this on a WP multisite on CiviCRM 5.20.0.
// Set USPS standardization
$civicrm_setting['CiviCRM Preferences']['address_standardization_provider'] = USPS;
$civicrm_setting['CiviCRM Preferences']['address_standardization_userid'] = ***;
$civicrm_setting['CiviCRM Preferences']['address_standardization_url'] = 'http://production.shippingapis.com/shippingapi.dll';
// Misc
$civicrm_setting['CiviCRM Preferences']['recaptchaPublicKey'] = ***;
$civicrm_setting['CiviCRM Preferences']['recaptchaPrivateKey'] =***;