[ecfisa]

Aca está.

Código Delphi [-]
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Grids, StdCtrls;

type
  TstringGrid = class(Grids.TStringGrid)
  public
    function GetEditText(ACol,ARow: Longint):string; override;
  end;

  TForm1 = class(TForm)
    StringGrid1: TStringGrid;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
  public
  end;

var
  Form1: TForm1;

implementation {$R *.dfm}

{ TstringGrid }
function TstringGrid.GetEditText(ACol, ARow: Integer): string;
begin
  Result := Inherited GetEditText(ACol,ARow);
end;

{ TForm1 }
procedure TForm1.FormCreate(Sender: TObject);
begin
  StringGrid1.Cells[1,1]:= 'Prueba de GetEditText';
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage(StringGrid1.GetEditText(1,1));
end;
end.

Funciona perfecto (Delphi 7).

Saludos.