How customized can an mfsroot be?

[Peter Steele]

>Can you write a few shell scripts?  You'ld need to create a tarball of the /var contents you need on the box, and explode it onto
> /var at boot time -- if you're using auto-var on MFS all the time, you'll need to set that up to happen on every reboot.

Obviously I can do that. What I was really asking was if there was a BSD option to do this automatically. I don't want to needlessly bloat the image if I can avoid it since this is to become a downloadable iso.