Ability to Change Developer's Name and Email
It seems that once you have created a Developer (or they have signed up), it is not possible for an admin/publisher user to modify the user's email address, first name or last name.
The user can change this themselves via Developer Portal, but no way for admin to do anything.
It can be changed via the API. Would that work for you?
Dan Byrne commented
Yes that is a reasonable workaround, for scenarios where we absolutely need to make user changes but cannot request this of the user.
It seems like a fairly obvious kind of admin user experience though, to be able to modify user details, so I would hope that this would be available via Azure Portal one day.