Visa Consular Appointment - Update Petition Expiration Date

[sanmo]

Hello,

I am having to make an unplanned, emergency trip to India and will need to go for H1B stamping. However, my H1B amendment is currently pending and has been upgraded to Premium Processing today.

1. I am planning to book a Visa Appointment. Since I do not have the approved I797 yet, I am planning to fill in some pseudo dates for Start and Expiration Date section while booking the appointment. Can this be updated later without affecting the appointment date once I receive the approved I797 (hoping everything goes well)?
2. If not, is there any other way to book the appointment to not lose the available date and avoid more wait?