The following question came up in the forum:  "How do I delete the custom work item type that I created?"  Tony Edwards posted the following.  One other thing that comes to my mind is to have a second server to use for experimentation before applying changes to the production server.

It is not possible in v1 [to delete work item types].  This question came up recently and Bill Essary gave the following guidance for mitigating the problem:

 Here are a few things that you can do:

 1)   Change the name of the type to something like “(Deprecated) Bug” so that users know not to use it

 2)    Add an attribute to the WIT that stops users from creating a new Work Item of that type.  If your initial workflow state is “active,” the attribute would be added to this transition

      <TRANSITION from="" to="Active" not=" "[global]\Team Foundation Valid Users">

[Update 8/21/06]  Unfortunately, work item types cannot be renamed in v1, so #1 above is incorrect.

[Update 4/17/09]  In TFS 2008, you can delete work items and work item types using the destroyWI and destroyWITD commands in tfpt.exe in Team Foundation Server Power Tools for 2008.