Please Help me its urgent

[forsite]

Hi
I am planning to chnge from company A to B.I applied for H1 transfer.I got receipt notice and I may get approval soon.So once I start work in company B and if I don't want to continue in company B ,is it possible to go back to company A,if they don't cancel my H1?

Is there any chance in H1 transfer after getting H1 transfer receipt,chance of disapproval of visa.

Can I start working as soon as I receive H1 transfer receipt notice or do I have to wait till visa get approved?

Please help me out