I always copied the changed profile to the default profile, also in Vista. But in Windows 7 it is simply greyed out so you cannot do this anymore.
After some research I found out it is not even supported to do it this way.
This article describes how you can do it correctly: http://support.microsoft.com/default.aspx?scid=kb;EN-US;973289
Briefly it tells you to run a sysprep with a answer file attached where the parameter Copy Profile is set to true. In the article you also find links to create the answer file in SIM (System Image Manager). I only couldn’t find the right component you have to you use in the Specialize pass of the answer file. To save you some time the component is named “Microsoft-Windows-Shell-Setup”.
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