H1b stamping with new 797 after transfer and future joining date

[Patni.harry]

My h1b change of employer is in progress with employer B and I have a extension with employer A till sep 2018. I am traveling in June 7th to India for vacation and visa stamping ( visa stamping is expired and anyways due for renewal). Once the transfer is approved employer B will send the petition to me in INDIA
1) I will be using the new 797 petition by employer B in ds160 which will have petitioner as employer B in visa stamp
2) can I stamp with employer B but with joining date in future 13th July

Thanks for your help in advance