EB-1A is self-sponsored, you can change your job within the same field freely. If EB-1b, you can't change your job, since it is employer-sponsored.
But you can't change your field of study, for example, you are a researcher, and you file your EB-1a, you can't be a computer engineer at the time of your I485 approval.
My colleague just got his EB-1a approved two months ago. Not very tough to get it.