The way I do this is a bit different.

For each activity (watching TV, watching DVD etc), I have a device with 4 pages. Each page is reached by pressing one of the four firm keys. The first 3 pages have the buttons for controlling the activity. I use the 4th page (reached from the 4th firm key) to fix things up such as power on/off, setting the correct video input. Once I've fixed whatever was wrong, I press the 1st firm key to get back to controlling the activity. Even with discrete codes, things can go wrong e.g. the power didn't go on.

Where I don't have discrete codes I have it set up so that the device is in a known state when I go to the Home page. For example, my DVD does not have discrete power. So, when I push the 'Watch DVD' button on the Home page, I turn the DVD on. Whenever I go back to the Home page from anywhere in the DVD activity, I turn the DVD off.