Just an example: OP during his cross examination stated that he crouched. He also stated that he held his firearm in a specific manner.
Up until he had stated those words, the state had no idea as to what he would be stating.
The state 'could' apply to re-open their case and recall Capt Mangena to the stand in order to question him about OP's firing position once again - as the state have only NOW heard, via OP's own forked tongue what that position actually was.
Capt Mangena got terribly excited whilst OP was describing to the court 'how he stood and how he was holding his firearm'.
I'm not saying the state will do the above - but I'm trying to give you an example of 'evidence that will be NEW for the state - that they could try and refute if they applied to re-open their case'.
The evidence the psychologist for the DT gives, will most certainly be grounds for re-opening the state's case. Of that there is no doubt. The state will be afforded the opportunity to call their psychologists once this door has been opened by the defense.
Oh, for sure about the psychologist. Never seemed fair to me that the prosecution couldn't rebut a psychologist's findings, among other things.