Two things to keep in mind, *I* don't do the resolution swapping. I know HOW to do this, but it gives very bad results. But there is a workaround. QuickTime 2.1 added a toolbox call named BeginFullScreen which would resize the video for playing movies. Each monitor is an island when using these calls. You can proceed to black out other monitors with the same call by passing their GDevices or you can ignore them (as I do). So basically, this is an actual toolbox safe way to a)hide the menubar and b) switch monitor resolution, and still be compatible. The only thing you lose while swapped is events must not be handled or the finder icons will get nutty.
If you pass as your screen resolution the current screen width and height for whichever GDevice you want to change, then only the menubar will be hidden and you can process events without worrying about the finder icons.
I think my point here is that this a MacOS 'feature' which probably nobody really uses, but it is there and it is quite safe and compatible as long as you follow the rules. I think that covers the 'not likely to work on every mac' situation. Since QT does all the hard work, I am hoping it does it correctly when talking to third party video cards, but its certainly possible it could fail. Often I have seen QT do nothing or swap to the closest resolution the card is capable of. The calls report back the screen's current width and height as opposed to what you asked for. Clearly this call cannot work with every monitor or card, but QT allows for fairly graceful handling of the situation and it is bad design to rely on 640x480 anyway.
The only really practical application I can think of for this is an arcade style game or a presentation app. Or in TJ's case the 6502 emulator.