Adding and removing extensionattribute to AD object

You could try using the -Clear parameter

Example:-Clear Attribute1LDAPDisplayName, Attribute2LDAPDisplayName

http://technet.microsoft.com/en-us/library/ee617215.aspx

I used the following today - It works!

Add a value to an extensionAttribute

 $ThisUser = Get-ADUser -Identity $User -Properties extensionAttribute1    Set-ADUser –Identity $ThisUser -add @{"extensionattribute1"="MyString"}

Remove a value from an extensionAttribute

  $ThisUser = Get-ADUser -Identity $User -Properties extensionAttribute1  Set-ADUser –Identity $ThisUser -Clear "extensionattribute1" 

I have struggled a long time to modify the extension attributes in our domain.Then I wrote a powershell script and created an editor with a GUI to set and remove extAttributes from an account.

If you like, you can take a look at it at http://toolbocks.de/viewtopic.php?f=3&t=4

I'm sorry, that the description in the text is in German. The GUI itself is in English.

I use this script on a regular basis in our domain and it never deleted anything or did any other harm. I provide no guarantee, that this script works as expected in your domain. But as I provide the source, you can (and should) have a look at it, before you run it.