I am on F-1 OPT status working with company A which expires on 6/28/2013. Company A filed for my H1B and I got I797A approved application in my hand with start date of Oct 1, 2013.

My question is:

1) Can I change employer to company B before Oct 1, 2013. If YES and if company B file new H1B will it be subjected to the H1B cap for year 2013 ?

2) How the revocation of the whole H1B process work from Company A and how it will effect Cap-Gap extension period?