Restlet error pages looks like this:
Is there a way to replace Restlet Error pages with custom template and/or redirect to another page (error html pages)?
There are two ways to that:
You can return either custom HTML, text or structured content like JSON leveraging Restlet converters.
This link could give you hints about the way to implement this: https://templth.wordpress.com/2015/02/27/exception-handling-with-restlet/.
Hope this help you. Thierry