somewhere there is a button then! maybe at another position, but there must be a button. stuff like traction control can always be switched of as for some situations you are better of without.
as far as the adding of ASC+T afterwards is concerned, it is possible. all you need is the correct parts and someone to do it. I am sure that it will be a major valet breaker, though. They would have to wire the whole car, get the sensors installed (maybe that needs extra parts again, new control sysytem as brakes and ignition are invoved....it will be a pain...