The experiment is incompletely specified. How would you measure the conscious experiences X and B?
Presumably you would have to ask the person what they experienced, and take their answer as fact. But their reporting of a difference in experience is a physical difference; words, noises, are physical events. So we find that the physical consequences of state A were different between times t1 and t2.
This difference in physical consequences could be the result of randomness in the setup of A, or inherent randomness in the laws of physics.
Or it could be the result of some mysterious non-physical influence - some soul guiding the person's behavior.
So, the experiment would still be inconclusive.
It would be more conclusive if you could also trace the entire physical chain of cause and effect that led from state A to the utterance "I experienced X" or "I experienced B." If this chain of cause and effect is in both cases entirely within our understanding of physics, this would be evidence against dualism. On the other hand, if mysterious things happen within this chain of cause and effect that do not fit within our understanding of physics, that could be evidence for dualism - or for a new breakthrough in physics.