It's good to know that you don't need EAD to use AC21 for job change. I was going to file for EAD and AP on my expense just in case If I have to change job.
BTW I found one interesting memo which says that you don't need to wait for 180 days after I-485 receipt date to change job. You can change job before 180 days of your I-485 receipt date. Here is snippet from yates memo published on May12, 2005
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Question 10. Should service centers or district offices deny portability cases on the sole basis that the alien has left his or her employment with the I-140 petitioner prior to the I-485 application pending for 180 days?
Answer: No. The basis for adjustment is not actual (current) employment but prospective employment. Since there is no requirement that the alien have ever been employed by the petitioner while the I-140 and/or I-485 was pending, the fact that an alien left the I-140 petitioner before the I-485 has been pending 180 days will not necessarily render the alien ineligible to port. However, in all cases an offer of employment must have been bona fide. This means that, as of the time the I-140 was filed and at the time of filing the I-485 if not filed concurrently, the I-140 petitioner must have had the intent to employ the beneficiary, and the alien must have intended to undertake the employment, upon adjustment. Adjudicators should not presume absence of such intent and may take the I-140 and supporting documents themselves as prima facie evidence of such intent, but in appropriate cases additional evidence or investigation may be appropriate.
