Gotta say all the outfit switches work quite well.

Since there are minase_akiko_(cosplay), okazaki_ushio_(cosplay) and the like, maybe we can add more ??_(cosplay) tags.
Personally I think Masato is cosplaying Kunisaki Yukito (and the bust of headmaster is cosplaying as his doll. Zen even made a comment that the 'doll' is controlled by muscle power)
Kyousuke is probably cosplaying Ootori Sakuya from Rewrite. Komari is probably Senri Akane from Rewrite (because Akane is the only one wearing black socks)
Mio is Kotomi from Clannad (but I'm not sure since the only distinguishable point is the book)
Kengo is Fujimaki from Angel Beats!
Riki is Nayuki from Kanon
While Rin is Misuzu from Air.

sakuraka_ama said:
Mio is Kotomi from Clannad (but I'm not sure since the only distinguishable point is the book)

She is the only one that wears dark kneehighs with her school uniform (post #183331), so that matches up too.