According to the official blog, the cast of Funakubo Hiroko
in Saki: Achiga-hen - Episode of Side-A
will be changed from Manami
to Misawa Sachika
. Seiyu Manami wanted to devote herself solely to the activity as a singer. Misawa will play Hiroko from Saki: Achiga-hen - Episode of Side-A Specials
. The first episode of the special will be aired on December 24th.
Source: Saki Anime official blog