Yeah, I'm not crazy about startup scripts that then modify other startup scripts. I've just tried chattr +i on it, so I guess I'll see if it breaks the next time there's an update (at least I'll know about it if it breaks). However, as a less bad solution, what about adding a "PERSIST_ON_UPGRADE" flag to that file, which the dpkg scripts check for? If it's set, then the upgrade shouldn't overwrite the file.