Switching modes like that was common practice on the Amstrad CPC (which used the same 6845 video chip), but as time went on, people also learned how to change the base address of screen RAM part way through each frame. This gave you super-smooth hardware scrolling for the main game area while still retaining a static score display. Unfortunately it came too late in the machine's history to be used for more than a handful of games, but demo coders used it extensively (and still do).