'Twas brillig, and the slithy toves did gyre and gimble in the wabe

Oh, I think KDE's own resolution changer can switch resolution on-the-fly (I had it start at 1024x768 instead of 1280x1024 before, and was able to correct that without logging out). Unfortuantly KDE's own changer is incapable of setting resolutions that it doesn't think are supported (or if it is, it requires mucking about with command-line tools - I should not need to use a command prompt to do basic system configuration)