H1B transfer before Oct 1 (current status: H4 visa)

hello, I am on H4 dependent visa, filed H1B from employer A. Hoping and wishing that my H1B approve, can I change the job to employer B before the start date? Also, Employer B is the start up business which will start only after my H1B transfer done to employer B.

Once your H-1 petition is approved prior to Oct 1, B can file a cap-exempt petition for you. Assuming your H-1 is approved w/ COS, you can join B from Oct 1 even if their petition is still pending.