Would a prediction be accurate if the person about to act becomes aware of the prediction prior to the act itself?
This is a classic problem of the deterministic approach to action. If psychology was perfect, it is likely that this would enable psychologists to predict how a person is going to act in any situation. It would also make psychologists able to predict when this act would take place. However, for such a prediction to be useful, the psychologist would have to keep this information from the subject. Otherwise, the knowledge of the prediction could potentially make the person act in a different way, rendering the prediction obsolete.
Does the fact that a prediction can be known in advance disprove the possibility of predicting accurately or is that fact just one more antecedent condition?
The fact that a prediction can be known in advance does disprove the possibility of predicting accurately. The moment a prediction is made, the prediction alters the state of the components that were necessary to know in order to make a prediction. Therefore, the prediction becomes obsolete as the action might or might not happen in the way that was previously predicted.
