your right about the unattend.xml file not helping on start up. the settings for many of those features are queued to happen on start up as part of the sysprep process, meaning it executes those commands before shutdown and before you extract your image. your problem seems simple though. instead of using the sysprep process to create your accounts write a script to create them on first startup, that would be easy enough to edit and you could guarantee that it ran after the first boot. also depending on your environment you could manage accounts using group policy