you can export the birthday calendar, and then import into another (or new) calendar.Then you will have an editable calendar.
試一下這個機器人workflow我都是用他建立有通知訊息的生日事件http://code.google.com/p/icalbirthdays/安裝到機器人後執行一次就ok了可以設定生日前幾天提醒+生日當天提醒