Unable to edit Domain Controllers computer set

Hello,

Can someone please assist me with how I can adjust the domain controllers that are listed in the Domain Controllers computer set?  I am using Forefront TMG 2010 on Server 2008 R2.

After doing some research I've come across a few posts leading to these links but they do NOT work:

• http://blogs.isaserver.org/shinder/2006/07/09/how-do-i-edit-the-domain-controllers-computer-set/
• http://forums.isaserver.org/m_200287500/mpage_1/key_edit%2cDomain%2cControll/tm.htm#2002009305
• http://technet.microsoft.com/de-de/library/cc441740.aspx

This is a predefined computer set that does not allow to make any adjustments and there are old DCs in the list that need to be removed.

Thank you to anyone who can assist.

Ryan