Teams for Education: Team Avatar

Dear community, is there a way to add custom pictures to the predefined list of avatars in Teams for Education? I can set the avatar by using Set-UserPhoto and the -GroupMailbox switch but we would like to give our users the possibility to select from set of pictures.

So I'm trying to add custom pictures to the ones shown in the screenshot:

I found this but it didn't really help: https://support.office.com/en-us/article/Change-your-team-picture-02ea2af6-b49d-4de8-9551-1a5e472993c0

Thanks!