My Perm is filed in October 2008 under EB3 and was audited. As per your current dates, guessing it might be approved in October 2010.
1. I would like to know if I can file I-140 under EB2 as I got my work experience eligible for EB2 category.
2. If I change employer before my PERM approval, will my priority date change? If so, to retain Oct'08 date, till what time, I can be with my employer?
3. Once I-140 is approved, can I change employer or stay for 6 months and then change employer so that my priority date will retain oct'08?
1. No. PERM application determines what your category is.
2. If your I-140 is not approved, you cannot carry your PD to a new employer.
3. Once approved, you can carry your PD, even if you leave earlier than six months. You do have to start your green card process all over again.