Due to the unique way the Xbox app handles file permissions within Windows, Xbox games cannot be added to the X1 profiles the same as regular games can. This is circumvented by using the current active app menu instead of the traditional .exe selection. 

1. To start with, the Xbox or Windows store game you want to add needs to be running before doing these steps

2. After starting up the game you wish to add, open the X1 Control Panel and click "Create new profile"

3. Tick the box next to the game you wish to add the profile for

      

4. Click, "Link Apps", then either customise the image and name of the profile to your liking, or just hit "Save"

Congratulations, you've now created a profile for the Xbox game and can modify it however you like.