> If you just pass init=/usr/bin/emacs on the kernel command line, you shouldn't need to do anything to undo it.
That didn't work. Maybe this is a bug in Fedora's initram, because it worked the last time I tried it (several years ago, and with an actual init program).
For those curious, I did manage to do it though, by popping open my initramfs and adding an explicit INIT=/bin/emacs after the code which sets the INIT variable. The result was emacs saying "cannot open /dev/tty" and bailing, and then the kernel panicked.