My status:
H1B valid till 2011
I-140 approved
I-485 filed and pending since 06/2007
Priority Date: 01/2007
EAD and advance parole approved but not being used for travel or for employment.

I have received a job offer that may not be similar to my existing job classification under I-140.

I initially wanted to use AC21 and maintain my I-485 while transitioning to the new job. If I am unable to do it due to different job duties then what are my options?

1. Do I need to refile perm LC again for this new position?
2. Do I then lose my priority date?
3. And what happens to the I-140 and I-485 applications?