EAD with new employer


I am on H1-B since Junly 2004 and have an approved I-140 in EB2-India category. I also have EAD since January 2012, all through the same employer. My H1 is valid until Sept 2013.

I am now planning to change my employer. The new position I am considering is a manager position with direct reports but in the same field (software development). I will still be doing development work so 50-60% of my profile will be the same. My original job responsibilities did not include people's management (when the GC was filed).

1) Can I use AC-21 for the change notification or will I need to refile GC? Is the new position considered similar?
2) Will it help if I get my H1 transferred with the new employer?

I do not want to loose my EB-2 priority date of Juny 2008. What are my options?

Indian Lady