hot mail,
not true. The only EB1 that is mostly independent from a job is subcategory Extraordinary Ability. It is so because this subcategory does not require a permanent job offer from a prospective employer. Therefore, applicants in this subcategory are generally not constrained with a requirement of keeping one employer throughout the whole mess... err... I mean immigration process.
Other two subcategories, Outstanding Researchers and Managers/Executives do require a permanent job offer from a prospective employer. Thus, they would not be able to change employers while AOS is pending if it wasn't for AC21. But AC21 is silent in their regard. May be it is not applicable at all, may be it can be used,.. I have no idea. That is only my suspicion that EB1/OR may not enjoy benefits of AC21 portability.
superlucky_1,
what I am suggesting to do is to confer with a lawyer who deals with EB1/OR for a living. EB1/EA and EB1/ME lawyers will not help. Perhaps, there is a loophole, which will warrant changing jobs without even mentioning AC21.