6 months after you filed I-140, you can change your job, but have to prove the new job title is equivalent to the one before. Otherwise, you will have problems to verfiy your I-485 status.
After you get your GC, you're supposed to continue working for your company. But nothing can prevent you from changing companies.
After you get your GC, you're supposed to continue working for your company. But nothing can prevent you from changing companies.