[NumLock]

Код:

type
  TForm1 = class(TForm)
    CanEdit: Boolean;

procedure TForm1.FormCreate(Sender: TObject);
begin
  CanEdit:=True;
end;

procedure TForm1.Table1AfterDelete(DataSet: TDataSet);
begin
  CanEdit:=False;
end;

procedure TForm1.Table1BeforeEdit(DataSet: TDataSet);
begin
  if not CanEdit then raise Exception.Create('Oops');
end;