While I was preparing VSTS instances for a training I was giving I had to add a list of 20 users in a Team Services instance. At the time I couldn’t find a way to do that from the web interface so I looked at the web api. Gave me the same results. After questions asks to MVPs I know, no better idea than adding them one by one manually. So I started to add them one by one. Then after some times moaning against Microsoft I asked myself and if they thought of it and considered “;” separators when adding multiple users? I than tried and it worked ! It also worked when you want to add a list of users as Project Administrators or any security level you want.
Here is an example of adding 3 users in one click. Just separate them with a semicolon !