Can you change your Army MOS after Basic Training while at AIT?

Nope. No chance at all. Chances are the recruit was steered away from Mental Health Tech because there were no class seats available for the next year.

In my experience, if there were enough class seats, everyone in the Army would be Dog Handlers, LPNs, and Radiology Techs, and everyone else would be Special Forces and Rangers. But the reality is that there are only so many positions for low density MOS's and only so many class seats a year to fill those positions.

From what I understand.....no, the Soldier cannot change it while IN AIT. The MOS can and will change if the Soldier in question fails the Medic Course. However, if the Soldier fails the MOS school, they will be reclassed to a new MOS based on the Needs of the Army. I also edited your TAG from the original one you had because that is for an element in Europe and not relating to MOS and AIT.

Hypothetically, if a thousand variables lined up perfectly while Jupiter was in retrograde? Yes.
Realistically and practically, no, it's extraordinarily unlikely.

Also, keep in mind the original MOS the soldier wanted is probably the ONLY one the needs of the Army would certainly NOT put him in. Otherwise, he'd have gotten it in the first place.

No, can only change it normally in the year prior to ETS.

Unless he has a phd or is an MD he is not qualified for therapist. What he might be talking about is mental health specialist. School for that is 20 weeks which includes the medic portion. I know because I was one before I commissioned. I did not have to attend the 2nd 10 weeks because I already had an MA Ed Psych guidance and counseling.

Only way is to flunk out of ait. Then you are at the mercy of branch. You could end up with something you don’t want

It is too late for that. This recruit will have to graduate, spend a couple of years in the MOS and when the time comes request to change that MOS. The military spends way to much money on training to Willy nilly allow people to change in and out. AIT is a long and expensive process, heck he will receive valuable training that he could apply to a return to the civilian world.

That isn't a real possibility. If the MOS changes at this point it is generally because the individual failed the original MOS training and is being re-classed to something else.