COS from H1B to F1, then H1B before status changed?

[vivianzz]

I'm on H1B right now and plan to go to grad school starting mid August. I have 3 years left on H1B. I'm considering changing visa status while staying in the U.S., and will quit my current job in early August. Recently I'm interviewing for a couple of jobs that may work out, if it does... can I cancel the change of status and apply for H1B for the new job? Does it matter if I would have left my current job? I understand the change of status will take 3 month or longer.
Also after being a F1 graduate student, can I change to H1B before graduating, (assuming there is a job offer)?

Thanks for helping me with the question in advance!