PD:Mar-2007
I-140/485 Receive Date@NSC: Aug 30, 2007 (Concurrently filed)
EAD-AP: Approved
Finger Printing: Done
I-140 approved: May 30,2008
I-485 RFE (on spouse H4) replied : July 23, 2008
LUD I-485 : July 29, 2007 (After sending RFE on H4, LUD updated on H1 & H4 cases).

I visited my home country, returned Jan 2009 on Advance Parole. My current I-797 is valid until August 25, 2009. My GC Sponsor company is not applying H1 extension since I have an approved EAD. I personally like to get & maintain H1 status.

1. Is it possible if I transfer my H1 to employer B (same job responsibilities & title) and use AC-21 to port approve 140 to the new employer without jeopardizing/affecting my GC process?

Please help me understand a use of AC-21 for H1 transfer.