There are conflicting statements on the internet about Anasui's sex and the reason it got changed actually.
The most popular among fans is obviously "Evil editors didnt like gay main character", but there are actually several bits of interviews out there where it was stated that the reason Anasui was made a guy is because the manga was overwhelmingly filled with female characters already. Apparently Araki or his editor decided they needed more men in the story, so they changed it last minute.
That little controversy aside, I never liked Anasui much. Especially not with Jolyne. And switching his sex won't change that for me.