How to change TFS Team Foundation Server template?

Install Team Foundation Server Power tool.
Then you will get Process Editor for changing TFS template.

http://visualstudiogallery.msdn.microsoft.com/c255a1e4-04ba-4f68-8f4e-cd473d6b971f

Process Editor


An add-in to the Tools menu, the Process Editor provides a graphical user interface for editing Team Foundation Server process templates inside the Visual Studio IDE. This tool also provides a GUI for viewing the values assigned to all fields defined in a project collection.