Hi, all!
Nice work. I did something similar a while ago; I posted it in
this thread. It's pretty much the same idea, but the implementation is a little different.
Basically it's a start.sh that calls the original start.sh by default. However, if it finds a lockfile, it first deletes the lockfile and then calls testing.sh
instead of the default start.sh.
This way, you can just create the lockfile (I use the command 'touch lockfile') and reboot. The iLiad will delete the lockfile and use the experimental start script. If the script fails, simply reboot and you're back to the original start script.
I like your idea of checking for an SD card, because then all your work can be done on the SD card. No need to use ssh to login or to manually create a lockfile, it's all just automatic. Nice work!