If you use the "fake device" method, and tell the Harmony that the device remembers which "input" (picture mode) it is on, and that there is no way to go directly to the first input, then the Harmony will keep track of what input it is on and switch it appropriately as you go from activity to activity. It shouldn't get out of sync if all goes well, and if it does, you'll be able to fix it using the "Help" button.

If you use the Activity start/end macro method and switch to a standard mode on activity exit, then if it gets confused, all you'll need to do is switch to another activity and then back to the one you want.