That may not be true myimmigration:
AC21 rule of 180 days applies to the INS not the petitioner. Which means that once applied for 485, if INS cannot adjudicate your case before 180 days ( which is very unlikely ), you can change your job even on the 2nd day of receive date. So, the consent of sponsoring employer is really not an issue at all. 485 is for future employment and for the Adjustment of Status of the applicant,,, the sponsor's role is very limited here.