I am working with employer A and my H1 visa is approved in consular notification with this employer but I have not gone for stamping to my hometown yet .i.e. I am still not on H1 visa.
Is H1 transfer to employer B is possible in this situation?
Legally, you can apply H1b transfer but chances of its approval are low with current USCIS scrutiny.
USCIS is sending RFEs to prove current H1B status before approving H1B transfer. You can prove status only if you have already been on H1B status.