assign TFS Workitems to different users

The following code display how it's possible to set the assign-to field from one user to another user. I had to write this code because in my instance the console command did not work:
TFSConfig Identities /change /fromdomain:Contoso1 /todomain:ContosoPrime /account:Contoso1\hholt /toaccount:ContosoPrime\jpeoples

Since the created-by field is a read only field this code will not change the value but if your really need to handle this then I think it should be possible to manipulate the XML of your Workitems and then handle it. Sounds to me like a lot of work.

Add the following using's to your classes:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using Microsoft.TeamFoundation.Client;
using Microsoft.TeamFoundation;
using Microsoft.TeamFoundation.Server;
using Microsoft.TeamFoundation.Framework.Client;
using System.Collections.ObjectModel;
using Microsoft.TeamFoundation.Framework.Common;
using Microsoft.TeamFoundation.WorkItemTracking.Client;
using Microsoft.TeamFoundation.VersionControl.Client;

Helper methods:

    public static string url = @"https://tfs.yourdomain.com/tfs";
    
    [System.Diagnostics.DebuggerStepThrough]
    public static TfsConfigurationServer GetTfsConfigurationServer()
    {
      return new TfsConfigurationServer(new Uri(url), GetCredentials(), new UICredentialsProvider());
    }

    [System.Diagnostics.DebuggerStepThrough]
    private static ICredentials GetCredentials()
    {
      return new NetworkCredential("user", "password", "domain");
    }
    
    [System.Diagnostics.DebuggerStepThrough]
    public static bool EnsureAuthentication(TfsConfigurationServer srv)
    {
      bool result = true;

      try
      {
        srv.EnsureAuthenticated();
        srv.Authenticate();
        result = srv.HasAuthenticated;
      }
      catch (Exception)
      {
        result = false;
      }

      return result;
    }

The main code to re-assign your workitem assign-to field over all TFS collections:

this code is stright forward without any add ons or so... enjoy

    static void Main(string[] args)
    {

      List<Identity> tfsIdentities = Helper.GetAllTfsUsers();

      Console.WriteLine("Connecting to Server: " + Helper.url);
      TfsConfigurationServer srv = Helper.GetTfsConfigurationServer();

      Console.WriteLine("Ensure Authenticated: " + Helper.url);
      srv.EnsureAuthenticated();

      srv.Authenticate();
      int counter = 0;

      if (srv.HasAuthenticated)
      {
        CatalogNode configurationServerNode = srv.CatalogNode;

        // Query the children of the configuration server node for all of the team project collection nodes
        ReadOnlyCollection<CatalogNode> tpcNodes = configurationServerNode.QueryChildren(
                new Guid[] { CatalogResourceTypes.ProjectCollection },
                false,
                CatalogQueryOptions.None);

        foreach (CatalogNode tpcNode in tpcNodes)
        {
          Guid tpcId = new Guid(tpcNode.Resource.Properties["InstanceId"]);
          TfsTeamProjectCollection tpc = srv.GetTeamProjectCollection(tpcId);


          // Do your tpc work here.
          Console.WriteLine("{0}", tpc.Name);



          // get a reference to the work item tracking service
          var workItemStore = tpc.GetService<WorkItemStore>();

          if (workItemStore.Projects.Count <= 0)
          {
            // go over the next project
            continue;
          }

          // iterate over the projects
          foreach (Project project in workItemStore.Projects)
          {
            Console.WriteLine("\tProject: {0}", project.Name);

            VersionControlServer versionControl = (VersionControlServer)tpc.GetService(typeof(VersionControlServer));
            TeamProject teamProject = versionControl.GetTeamProject(project.Name);
            IGroupSecurityService gss = (IGroupSecurityService)tpc.GetService<IGroupSecurityService>();
            Identity[] appGroups = gss.ListApplicationGroups(teamProject.ArtifactUri.AbsoluteUri);

            foreach (Identity group in appGroups)
            {
              Identity[] groupMembers = gss.ReadIdentities(SearchFactor.Sid, new string[] { group.Sid }, QueryMembership.Expanded);
              foreach (Identity member in groupMembers)
              {
                if (member.Members != null)
                {
                  foreach (string memberSid in member.Members)
                  {
                    Identity memberInfo = gss.ReadIdentity(SearchFactor.Sid, memberSid, QueryMembership.None);

                    if (memberInfo.Type == IdentityType.WindowsUser)
                    {
                      // Console.WriteLine("\t" + memberInfo.AccountName + " - " + memberInfo.DisplayName + " - " + memberInfo.Domain);
                      if (!tfsIdentities.Contains(memberInfo))
                        tfsIdentities.Add(memberInfo);
                    }
                  }
                }
              }
            }

            WorkItemCollection workItemCollection = workItemStore.Query(
                    " SELECT [System.Id], [System.WorkItemType]," +
                    " [System.State], [System.AssignedTo], [System.Title] " +
                    " FROM WorkItems " +
                    " WHERE [System.TeamProject] = '" + project.Name +
                    "' ORDER BY [System.WorkItemType], [System.Id]");

            foreach (WorkItem item in workItemCollection)
            {
              counter++;

              bool containsOldDomain = item[CoreField.AssignedTo].ToString().Contains(@"OldValidUser");

              if (containsOldDomain)
              {
                WorkItem item1 = workItemStore.GetWorkItem(item.Id);
                item1.Fields[CoreField.AssignedTo].Value = "NewValidUser";

                try
                {
                  bool a = (item1.Validate().Count == 0);

                  if (a)
                  {
                    Console.WriteLine("\t\tValid: " + item.Id + item.Title);
                    item1.Save();
                  }
                  else
                  {
                    Console.WriteLine("\t\tNot Valid: " + item.Id + item.Title);
                  }
                }
                catch (Exception ex)
                {
                  Console.WriteLine(item.Id + ": " + ex.Message);
                }
              }
            }
            // clear users
            tfsIdentities.Clear();

          }
        }
      }

      Console.WriteLine("Workitem count {0}", counter);
      Console.WriteLine("Press enter to exit");
      Console.ReadLine();
    }