Per a request from @SNg_WMF, Trust-and-Safety want to be able to do oversight (suppression) training with other colleagues in T&S and in WMF Legal. This is just going to be test content, so nothing sensitive.
To be able to do this, they need to be able to add people to https://test.wikipedia.org/w/index.php?title=Special:ListUsers&group=suppress which currently no one can currently add anyone to that group.
While createAndPromote.php can be used, this isn't very user friendly, nor is scalable.