You can turn them on and off from the Customize dialog's list of keys. That's the quickest way.
But if you have to keep turning them on and off, and can't use them in every program, it largely defeats the purpose of them being global.
In case of any confusion, global hotkeys aren't needed if you only want the hotkey to work while Opus is the active window; normal hotkeys do that job and won't get in the way of other programs.