just my opinion

First, I don't know how much your switch in area is. Sometime what we professional will consider a switch may not be a one for immigration purpose. E.g. a postdoc in a biomedical reserch institute get a position in a consultant co, as a manager. To us it is a totally irrelevent position. However, if your new position still somewhat (to the degree you can convince immigration officer) related to biomedical, it is considered within the area, thus fine. So check with your lawyers, whether you can do this.

If you really switch field (say from biomedical to boat saleman ;-), you have to have your fingers crossed. Since lots of time, they will approve your 485 without interview or any contct to you. Then no problem. Otherwise, if they check what you have been doing in between 140 appoval and 485 interview, then, no matter EAD or H1, you have to explain why you are still considered in the field as of 140. Thus, by swtich from biomedical to boat saleman will be very hard to justify.

I think you get my opion. I am not a attorney, thus all what I am writing is for my entertainment only. Haha.