As I mentioned in my previous posting, the Microsoft Visual Team System Process Editor was based on the ImagiNets Work Item Editor tool. The tool was originally a standalone application, but with Alan Wills' help, we integrated the tool into Visual Studio as a VS Package. We also replaced the work item workflow editor with a visual designer.
This tool allows you to edit process templates downloaded via the TFS Process Template Manager. You can also edit work item type definitions in live projects. Naturally there are limitations. Editing a field's type is not supported if there are work items created using this field. You can, however, add new fields without restriction.
The Process Editor will be shipped in the next release of the Team Foundation Power Tools (formerly Power Toys). I expect this to be released in the February 2007 time frame.