[dr. F.I.N.]

Код:

var
  S: TstringList;
  st: String;
begin
  S := TStringList.Create;
  S.LoadFromFile('<FileName>');
  S.Text := StringReplace(S.Text, '_O_', '<NewText>', [rfReplaceAll, rfIgnoreCase]);
  S.SaveToFile('<FileName>');
  S.Free;
end;