Once you have configured the custom relationship permissions, you will have the ability to give this custom relationship visibility into manager level custom attributes that you have set up previously. 

To view this, the person who has been given this visibility and applied this custom relationship, can go to the "You" page of the user they now have visibility into. From here, they will be able to click on the "Details" section of that person's You page, and view that custom attribute, as shown below!

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