How to put a cell in overstrike mode so characters get replaced instead of inserted as you type

This can be achieved by using TextBox.SelectionLength property of GridTextBoxCellRenderer in CurrentCellKeyPress event. The idea to achieve this is by selecting one character when a key is pressed, and also neglecting the Backspace key.

private void gridControl1_CurrentCellKeyPress(object sender, KeyPressEventArgs e)
{
   GridTextBoxCellRenderer cellRenderer = this.gridControl1.CurrentCell.Renderer as GridTextBoxCellRenderer;
  
   if(e.KeyChar != Convert.ToChar(Keys.Back) 
    && cellRenderer.TextBox.SelectionLength == 0)
   {
	   //Programmatically selects One char.
       cellRenderer.TextBox.SelectionLength = 1; 
   }
}

private void gridControl1_CurrentCellKeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
  if(e.KeyCode == Keys.Back) 
  {
	   //Translates the Backspace key to a left arrow key.
       SendKeys.Send("{LEFT}"); 
       e.Handled = true;
  }
}
Private Sub gridControl1_CurrentCellKeyPress(ByVal sender As Object, ByVal e As KeyPressEventArgs)
    Dim cellRenderer As GridTextBoxCellRenderer = CType(IIf(TypeOf Me.gridControl1.CurrentCell.Renderer Is GridTextBoxCellRenderer, Me.gridControl1.CurrentCell.Renderer, Nothing), GridTextBoxCellRenderer)

'Programmatically selects One char.
        If e.KeyChar <> Convert.ToChar(Keys.Back) AndAlso cellRenderer.TextBox.SelectionLength = 0 Then
cellRenderer.TextBox.SelectionLength = 1 
        End If
End Sub

Private Sub gridControl1_CurrentCellKeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms. KeyEventArgs)
   If e.KeyCode = Keys.Back Then
'Translates the Backspace key to a left arrow key.
      SendKeys.Send("{LEFT}") 
      e.Handled = True
   End If
End Sub