[Lucas Malor]

I have not understood well... with "shell" do you mean script? Do you want to automatically invoke a script at startup, and reinstall it easily after every firmware upgrade?

If so, to run the script at startup you have only to add it to the rcS file. About reinstalling the hack, take a look to the source code of the Night Mode hack: yoq had implemented a simple way to do it.

I suggest you to _not_ put under /mnt/onboard the script and any other file your hack will use, since they could corrupt your database (see Night Mode thread).