Is it possible to do a second hair transplant 6 months after the first session, in new recipient area?

The second recipient site should be different than the first.   If a strip procedure were performed at the first procedure FUE may be required if there is not sufficient skin laxity.  If FUE was performed at the first procedure there should not any limitations on the donor area at six months.  

It is best to ask your surgeon about a second surgery.  In general you should wait until the hairs have grown out from your first surgery.  This takes up to one year.

There is no problem with doing second procedure after 6 months interval between 2 transplants. Especially since you are transplanting into a virgin area of the scalp.

You should consider a few factors:
1. You would like to see the final result of the first procedure both to gain trust in the surgeon and to know how to plan the next one.
2. If it is a second FUT, then you must check if your donor area has softened and laxity come back.
3. If it is a second FUE, then you have to make sure the donor area has recovered. This is more likely if the first session was a moderate one, lets say not more than 2000 graft. If it was a 3000-4000 graft procedure, I would wait at least 12 months.

Yes, it is possible to perform a 2nd surgery in a different area after 6 months PO. It depends which donor harvesting technique (strip or FUE) was originally used and how many grafts can be available to achieve the new surgical plan. I recall performing back to back (4-6 weeks apart) hair transplantation 12-15 years ago with donor strip technique without problems and complications.