Thanks both. I had had a look for a built-in feature for CSS previously and hadn't found it, but I've had more luck on a second attempt. Looks like I should be able to get what I need with the existing features.
I'm aware of the patcher. However, I'd like to avoid using it if possible, as it'll complicate firmware updates. Still, I'm a software engineer myself, so if I have time to play at some point, I may well do
