Question about changing VISA type during greencard application

I am having a position as postdoctoral scholar in Univeristy with H1b visa. I am applying for NIW while have a plan to go back to school as soon as possible if I can. My question is that can I do it without the change of visa type or do it with the change of visa to F1 without affecting my greencard application. Or the question could be when can I go to school, even a medical school as I am doing research in the medical school, during the application of greencard.

Thanks a lot.