Thread:Project:Support desk/Customizing interface messages using PHP files

Hi, I'm trying to run a family of websites using MediaWiki and would like to customize the interface messages on all of them. The customized messages on all of them should be the same. Is there an easier way to do this by including a PHP file instead of editing the MediaWiki: namespace message on all of the websites? I'd rather not modify the default MessagesEn.php file because that gets overwritten on upgrades. Thanks