C#

[DllImport("User32.dll", SetLastError = true)]
static extern bool GetComboBoxInfo(IntPtr hwndCombo, out COMBOBOXINFO pcbi);
		
[DllImport("User32.dll", SetLastError = true)]
static extern bool SetWindowText(IntPtr hWnd, string lpString);


struct COMBOBOXINFO 
{
	public int cbSize;
	public RECT  rcItem;
	public RECT  rcButton;
	public int stateButton;
	public IntPtr hwndCombo;
	public IntPtr hwndItem;
	public IntPtr hwndList;
};


struct RECT 
{ 
	public int left; 
	public int top; 
	public int right; 
	public int bottom; 
};

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COMBOBOXINFO comboBoxInfo = new COMBOBOXINFO();
comboBoxInfo.cbSize = Marshal.SizeOf(typeof(COMBOBOXINFO));
GetComboBoxInfo(this.Handle, out comboBoxInfo);	
		
SetWindowText(comboBoxInfo.hwndItem, item.Text);