Using the same procedure as before, I changed the first byte of the pmcstore.edb file. Upon reboot, the zune works, and I browsed the system settings. Shut it off, look at the db file again - we have the first 4 bytes changed. No verification? I don't know, and want to find how badly I can break this file (and in what ways) before it stops working. It would be easier if I knew the format for this db. EDB is a common extension - exchange uses it, as do several 3rd party vendors.
Side note: I'm trying to keep up with the various zune forums, rockbox, libmtp, and of course, http://zune-linux.com/ (I post as 'cross' there). Other handy reading material on msdn, and xda developers forum.