Is it possible to boot up Android so flight mode is activated?
When I set airplane mode before rebooting or creating a nandroid backup the setting will stick.
Are there any files like init.d that are easy to modify where these kinds of boot options are stored?
Another alternative would be a modified Custom Recovery. But I haven't heard of one.
Restore an old Nandroid Backup, but before the system fetches all the updates (messenger...) the user wants to restore certain app data so nothing gets lost.
That is only possible when in flight mode.