Changing job while I-485 final processing is underway

I am working with employer A at a client site in Client B.
My I-485 came up for processing and I am submitted my docs for Supp-J, medical and so on. While waiting for the approval, my client B wants me to join as FTE since contract is ending.
My I-485 was filed in 2012. I have my EAD.
I am expecting my I-485 to be approved by end of the month.
1. How soon can I join my client?
2. Will starting the transition while approval is pending cause any issues?
3. Can I use AC21 to port while the final approval is pending?

I between a rock and a hard place as to what to do. Please help!



Registered Users (C)
You are OK to switch employer 180 days past of I-485 filing based on AC21 & submit new I-485 Supplement J should USCIS asks under AC21 portability clause.