I know
RCCL won't accommodate any adjustment after PIF date, and I'd be surprised if others would as well. That is the point of the PIF date and cancellation penalties. What RCCL will do, however, is let you upgrade cabins using the new rates. So, let's say you are booked in an outside, and the balcony rate drops after PIF, you can upgrade to the balcony at the prevailing rate.