Is there a policy or regulation on contacting HRC for possible open assignments after AIT?

Are you worried you will be sent to somewhere sucky? Already on orders and not liking where you will be sent? Sure, you can try and contact Branch. But, if you are an IET Soldier, be prepared to be told that you are going where you are assigned to. It is rare for an IET Soldier to get their assignment changed while in AIT. If you are talking about PS/MOS-T recalssing and are now on assignment, I believe that is usually TDY En Route. Good luck getting those orders changed.

Be a soldier and just train and go where your orders send you.

If I am not mistaken, you are an in service reclass, right? You were on here posting about different reclass MOS's before. You said you are two months into a 9 month MOS, meaning you PCS'ed to your AIT.

Your Branch Manager assigns your next location. If they say don't contact them, then don't contact them. As far as your BM is concerned, you are just another initial entry Soldier, and they are filling slots that need to be filled. They fill holes with the guidance and priorities they have been given. Even if you have a req number, you don't know if it is coded for a HAAP returnee, a compassionate reassignment, a nominative assignment, a special assignment, if it has been filled already, or if your branch has no intention of filling it. The assignment process is long, involved, and has about 20+ validation steps in it. Your branch manager can't even remove you from one assignment to move you to another without an exception to policy from their boss. Unless you have a valid reason you absolutely CAN NOT fill that assignment, or the Army needs you for a higher priority assignment - you are going on the assignment you received.

Unless you can explain to a full bird Colonel why the Army needs to put you into a different assignment, then you are keeping your assignment, because that is what your Branch Manager has to do to switch your assignment.