Topic on Extension talk:HeadScript

... which might be easier but also might cause problems, you could just add this to your LocalSettings.php:

$wgHooks['BeforePageDisplay'][] = function( OutputPage &$out, Skin &$skin ) {
     $code = <<<'START_END_MARKER'
<script></script>
<script></script>
<script></script>
START_END_MARKER;

     $out->addHeadItem( 'my-wonderful-script', $code );
     return true;
};

It does exactly the same thing as this extension.

This grays out everything afterwards in LocalSettings.php in MediaWiki 32. Any idea how to fix?

The following snippet worked for my version when the code above didn't, no plugin needed. Snippets/Load an additional JavaScript or stylesheet file on all pages