Short answer:
Depending on your country, the answer will vary. In certain countries, you don't need to have an OFC every time you apply for a visa. The website should automatically skip the OFC page, but if it doesn't do that I'd recommend reaching out to someone at the embassy either in-person on via the phone.
In other countries, the US embassy supports walk-in appointments if your situation is suitably dire and thus you also don't need to reschedule an OFC.
However, in many countries, the deadline for re-scheduling the visa appointment is 24 hours before the OFC appointment. This means that after your OFC, you cannot reschedule the visa interview. Many people, as a result of this, schedule their OFC as close as possible to the visa so that they have as much leeway as they can. If you end up missing your visa, you can reschedule both at a fee and that is your only remaining option, sadly.
Here is a sampling of the raw information I've collected. It's extremely contradictory and seemingly senseless because it is from multiple countries. I'd suggest doing more research to see what your country's guidelines are:
From this website: How to Reschedule a US Visa Appointment?
To reschedule a US nonimmigrant visa appointment, you can either call
the VAC or change the date and time online. You
must provide a valid reason as to why you are rescheduling so that the
US Embassy takes it into account.
To reschedule a US immigrant visa appointment, you must contact the
NVC and explain your reasons for wanting to reschedule. You must
provide your case number or application number and let them know of a
time that is convenient for you so they can try to get you that
appointment.
If you reschedule more than once, then you
may be required to pay a new visa application fee as a penalty.
This site suggests that the maximum number of times you can reschedule is actually two. Further,
If you need to travel urgently, miss your pre-booked appointment, or
simply cannot book an appointment at your preferred date and time, the
Walk-in Without Appointment service, available for select countries,
allows you to submit your visa application on a day you choose.
As per this site:
Yes, it is possible to reschedule your VI if your OFC has already been
completed. If you login to your Applicant Homepage, you will see a
'Reschedule Appointment' Tab which will directly show you the
available slots for Visa Interview, by skipping the OFC appointment
page, since your OFC will already be completed.
From this site:
Yes, you can reschedule if you have missed your appointment date and
interview.
Your application will be marked as ‘NO SHOW’ after 24-48 hours of your
scheduled interview date, and then the rescheduling option will be
available to you.
Please note if you are rescheduling the appointments, you may have to
reschedule both (OFC and Visa officer) the interview again.
You can log in to your profile on www.ustraveldocs.com for
choosing the available date for rescheduling your interview.
