剛查了一下可以透過BTT搭配Apple Script來達到這個目的，方法如下：
Step 1. 在BTT裡面把Predefined Action設定成"Run Apple Script in Background"
Step 2. 貼上Apple Script如下：
tell application "System Events"
tell process "SystemUIServer"
tell (menu bar 1's menu bar item 1 whose description is "text input")
click
tell menu 1's menu item "注音"