I was on my phone last night, so I had a hard time typing out details...
You can book the last 2 nights (10/30 & 10/31) as a split/separate reservation, but not as FD. FD requires a 3 night minimum. Also, additional FD reservations (or splits) must be booked by tomorrow when FD ends.
..."rolled into the FD package,"...umm, let me explain: a GS CM can modify your dates on an existing FD reservation. However, they will have to access the FD pool in the system; plug in your exact dates (like a new reservation), and your exact dates must show availability. They can't just tack on days. Does that make sense?
For example:
10/25 - 11/2 may show availability.
10/30 - 11/2 may show availability.
10/25 - 11/1 may not.
Exact dates must show availability in order to qualify for modifications.
They used to be able to easily trim off days without plugging exact dates into the system, but they don't do that anymore.
So unless BC becomes available by tomorrow for you to easily modify yourself online, it will take a little effort to keep calling and checking back.
I hope this answers your question
