How to configure Extension of a PageType so that the templates of the extension are choosen for render

SS4

I want to extend an pagetype with an Extension. I need to do changes on the template files aswell.
How do I have to configure the new modul so that the template of this new extension-module are taken instead of the orignal ones.

Thanks in advance
Fabian

// Include any relevant code. If you have a lot of code, link to a gist instead.