Yes. We only asked once. In our case, I missed my FP. (We changed hotels. I sent everyone ahead, while I took care of transferring luggage. ) The CM was great!
You are welcome! I probably shouldn't give all this away, but...
We were able to text the CM with our next FP request the moment we scanned our magic bands. DH was great! As soon as our bands were scanned, he hit send. As the week wore on, and we got better at creating smart requests, we often had our next FP while we were still in the queue! In a manner of speaking- we had our next FP BEFORE we'd finished using the last.
Guests can't use a kiosk until AFTER they exit the ride, locate a kiosk, walk to the kiosk, stand in line, etc. Using the kiosks is longer than just the kiosk line: it is the sum of the parts. Add afternoon temps in the upper 90's while we were there!
On our MK days, once we used our three FP, we spent the rest of our park time using one FP after another, except when we chose breaks. We had loose plans to break by 2pm, but it was hard to leave with continuous FP's.
No, the CM's can't get what isn't available, and that's a significant limit. By late afternoon, all Mt FP were gone. At Epcot, FP for Soarin' were gone by the time we used our 3FP, but we had a late start that day.