Much like some of the group settings can only be applied via PowerShell (see my previous post), so are some of the user attributes. For example, the value of Assistant attribute can not be set via management portal, but using Powershell will do the trick. Here's sample statement:
set-user -identity [User's email address] -AssistantName "[Assistant's Name]"
To view object properties before and after, use the following:
[User's email address] | format-list