Yes, dashboard is read-only. If you were to send commands back to the robot, then the laptop could operate as an outboard processor and would effectively be part of the robot. (Boy, wouldn’t that just blow your budget out of the water!)
That said, and on the subject of dashboards… the rules state that the Dashboard port can be used to feed “a computing device” for operator feedback. So, if you can’t afford a laptop, a Basic Stamp connected to an Epson LCD display and some lights would essentially cover the requirement as long as the assembly were self powered (batteries).