The usual way to make something "high priority" is to put it on the beginning of the Queue instead of on the end. This forces it to be the next thing that is dequeued, a "Do This First!!" instruction. That's the purpose of Enqueue Element at Opposite End. Some of the banter between natasftw and me was about using this function, which I called "Push", as this turns the Queue (a First In, First Out structure) into a Stack (a Last In, First Out structure). Of course, if you "mix metaphors" by putting high priority items at the front of the Queue, it becomes "something else", namely a "Queue with a High Priority Input" ...
Bob Schor