[Julià T.]

puedes aprovechar el BeforePost y el AfterScroll para cargar y guardar los datos

procedure TForm1.T1BeforePost(DataSet: TDataSet);
begin
 Re.a:=100;
 Re.b:=110;
 Re.c:=120;
 Re.d:=inttostr(t1num.value);
 with TDBISAMBlobStream.Create(T1aaa,bmWrite) do
 try
  Write(Re,SizeOf(TRe));
 finally
  Free;
 end;
end;

procedure TForm1.T1AfterScroll(DataSet: TDataSet);
begin
 with TDBISAMBlobStream.Create(T1aaa,bmRead) do
 try
  Read(Re,SizeOf(TRe));
  label1.Caption:=Re.d;
 finally
  Free;
 end;
end;