Yes, add the following to the config.inc.php file :
$config['reply_mode'] = 1;
That sets the server default to top-posting. (0 is bottom-post, -1 is don't quote)
You may want to read through the defaults.inc.php file to see what other configs you have control over at the server level - there are many. But do not make changes in the defaults file, always copy the line from defaults to config and make your changes there. That vastly simplifies future maintenance and upgrades. You defaults.inc.php should always be exactly the same as it was when you installed the package.