I would create a sub domain. Use Newproduct.XName.com
That way it can be a branded website. This way you can keep the new name under new UI and not confuse the existing users.
By keeping under sub domain you can also pass the domain authority of main. if they are different product or services I would recommend Silo each other. if you need help how to solve I can offer free consultation on this platform. In Return for a good review as a teacher.