procedure SwapMouseButtons(const ASwap: Boolean);
Begin
  if ASwap then
    SystemParametersInfo(SPI_SETMOUSEBUTTONSWAP,1, Nil, 0)
  else
    SystemParametersInfo(SPI_SETMOUSEBUTTONSWAP,0, Nil, 0);
end;
 
 
procedure TForm1.Button1Click(Sender: TObject);
begin
  SwapMouseButtons(True);
end;