I haven't tried /hotbar copy, but it does sound very useful, especially with the situation you described! Most of the time I only use the keyboard for 1-2-3-4, and use the mouse for everything else. Changing my main bar depending on what combo I want to perform sounds like a very good way to prevent those "Eek where is my cursor!?" and "Noooo my hand is too small! Is it 5 or 6 ? I guess we'll see!" moments