The loan paper talks about the difference between snapping the 5YHM CAS at various dates....at amendment date (for the loan), at each interest period, at a switch trigger date or at cessation. However this may be a moot point quite soon anyway....if CAS is fixed by an announcement in Feb / Mar 2021, then that is the fixed CAS for everyone referencing 5YHM methodology anyway from that moment on.
The forward rate would still be different from that fixed 5YHM rate, but as the time running up to end 2021 diminishes the difference between the spreads using those two methods is likely to narrow. So in practical terms it may not make a great deal of difference which method is used, and perhaps the main question is more what timing will suit you.
One thing looks certain, the pace is about to pick up. Protocol effective date, fixing spread adjustment, certainty on cessation date, news on tough legacy....all falling into place in Q1 2021. Expect active transition to pick up.