方法一：

#region 登录部分
private void RtnLoginOK_Click(object sender, EventArgs e)    //登录按钮单击事件
{
    this.Hide();
    FrmRoutineMain formRtnLoginOK = new FrmRoutineMain();    //新建主窗体
    formRtnLoginOK.ShowDialog();
}
#endregion
 
#region 切换用户
private void RtnMainSwitchUser_Click(object sender, EventArgs e)    //切换用户按钮单击事件
{
    if (DialogResult.Yes == MessageBox.Show("您确定要退出登陆吗？", "提示", MessageBoxButtons.YesNo, MessageBoxIcon.Question))
    {
        System.Diagnostics.Process.Start(System.Reflection.Assembly.GetExecutingAssembly().Location, "+自己程序设置的启动参数，没有则省略");
        Process.GetCurrentProcess().Kill();
    }
}
#endregion

方法二：

#region 登录部分
private void RtnLoginOK_Click(object sender, EventArgs e)    //登录按钮单击事件
{
    this.Hide();
    FrmRoutineMain formRtnLoginOK = new FrmRoutineMain();    //新建主窗体
    formRtnLoginOK.ShowDialog();
}
#endregion
 
#region 切换用户
private void RtnMainSwitchUser_Click(object sender, EventArgs e)
{
    if (DialogResult.Yes == MessageBox.Show("您确定要退出登陆吗？", "提示", MessageBoxButtons.YesNo, MessageBoxIcon.Question))
    {
        StartExe(Application.ExecutablePath);
        Thread.Sleep(1000);
        Application.ExitThread();
    }
}
 
private static void StartExe(string appName)
{
    string path = appName;
    Process ps = new Process();
    ps.StartInfo.FileName = path;
    ps.StartInfo.Arguments = "-routine";
    ps.StartInfo.CreateNoWindow = true;
    ps.StartInfo.WorkingDirectory = Path.GetDirectoryName(path);
    ps.Start();
}
#endregion