The app/loader.php loads all the needed core files for all the system's functionality. That said, this loader.php file allows you to add custom hooks which is actually any code you want to add:
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So is easy as create an app/chevereto-hook.php file to add new functions in the CHV namespace. It can be also the CHV\Render namespace or even G\ namespace. Sadly in PHP you can't override functions so the only workaround is to stop G\ from load default app functions and use your own.