Do I need REF if I change to part time H1 from full time H1

I'm currently a fulle time H1 and am thinking to switch to part time, and I know part time H-1B and full time H-1B are different(I don't know exactly what is the difference though)
So I wonder if I switch to part time, do I need to inform the immigration center?
A related question is if I dont switch to part time H1, and simply use my EAD, do I still need to inform the immigration center?


Thanks a lot!