The Frog's box will go from 230 to 250 kt because its a bloody computer - so
after reaching ALT CST it will immediately revert to 250/10000. Just because
the APP PHASE is only a mile or two ahead doesn't mean shmik to it. Its NOT
a pilot but a computer.
In your scenario I would've already reverted to OPEN DES to avoid a sudden
dramatic powerup, and pegged 230kts and activated the APP phase when I
decided it was time to. Anti-icing procedure is constituted during the descent
and the only time I've ever increased power to shed ice off the blades was in
a Navajo many yonks ago.
If a cadet flew a 320 like the FMC does I'd fail him.