Unfortunately DOWN hotkey can not be disabled or reassigned.
This was working on previous models, but is not available on FR945. Being able to disable or change function for the DOWN key (not all of us need it to launch only music) is an important feature. Even START+DOWN is present, but only DOWN shortcut isn't. Also we had this option in the previous FR935 watch.
Former Member, please bring it back in future FR945 updates.