You may not even need to cancel for an FFC and start a whole new booking since you can probably just use the change flight feature to get the AC flights that you want. Just make sure you get the same pricing as if you were doing a new booking. If you don't then you can revert back to cancel for FFC and then start a new booking. I personally just find it easier to do "change flight" to what I want, provided that the pricing remains the same.