Changing the main ip address of a tmg can result in many problems, like :
– some Forefront Services take long time to start up
– errors in the forefront console
– no network adapters in the forefront console

Here is how to change the Ip Address successfully:

– Change Ip Address(es) in the Windows System
– Change Ip in TMG Console -> Firewall Policy -> Network Objects -> Computer Sets – Array Servers
– Change Ip’s in SQL Server Configuration manager -> SQL Server Network Configuration -> Protocols for MSFW/ISARS
-> TCP/IP -> IP Addresses ( only if TCP/IP is Enabled )
– Start Administrative Tools -> ADSIEDIT
Connect to:
Connection Point (type):     CN=FPC2
Computer:                         HOSTNAME:2171
Navigate to:   CN=FPC2 -> CN=Array-Root -> CN=Arrays -> CN={UUID} -> CN=Servers -> CN={UUID}
(class: msFPCServer)
Open Properties and change the   msFPCIntraArrayAddress
– wait about 20 Minutes ( replicate adsi edit changes to registry )
– Search the Registry for the old Ip Address and change it
– Reboot