Since no one has replied ...
The openwrt forums list a failsafe way to boot the router: https://forum.openwrt.org/viewtopic.php?id=338. (hsmm is running on openwrt, but I don't know whether this will work for sure.) (Note that there is a response to that posting that suggests using mount_root.)
At the bottom of that page, there is a response that indicates that if you connect a serial cable to your router's serial port, you can interrupt the boot during the boot process, and not have to enter a password.
fyi,
robert |