The problem is that you can bork the menu enough to cause the watchdog to force a reboot, after which you're stuck in a reboot loop. You can probably use R&D mode to get out of that one, but I've not tried - I went to the trouble last time of putting my menu files into MyDocs, so I could access them in mass storage mode. Unfortunately the security changes in PR1.2 mean that won't work any more.