Currently I'm searching for a possible solution to apply 2 Physical Renderers in the manifest on 1 applet. Is it possible at all? If so, do I have to extend one file with the other?
You can definitely use multiple Physical Renderers on a single applet by extending one of your PRs with a second one. Make sure that you define your Manifest Files in the correct order. To do that set the sequence number of your base PR to 1 and the extending PR to 2. Without a specified order you are likely to get dependency issues.