The full script is available at
https://bugzilla.redhat.com/show_bug.cgi?id=448030#c41

[Patch 2/5]
Author: Frederick Grose <fgrose@sugarlabs.org>
Date:   Thu Apr 14 09:48:41 2011 -0400

    Support refreshing of attached LiveOS devices.

    Provide a new feature to refresh an attached LiveOS source image with a
    renewed rootfs and freshed overlay and, optionally, skip building a new
    .iso file.

    Updated base_on() to support selinux contexts, provide a liveos_mount()
    function, new functions to check disc space for building and refreshing
    (with an extra space option to test or adjust staging space). Provide
    an option to bypass the break to shell or script to permit uninterrupted
    processing. Include the kernel architecture of the source in the .iso
    image name, support F15-style rd.luks=0 in the boot configuration
    adjustment, and provide updated usage statements.

Unfortunately, the recent (09 April 2011, on my image) rsync update from 3.0.7-3.fc14 to 3.0.8-1.fc14 has broken the behavior for this application
such that symlinks do not get the right SELinux context. For example,
/lib/ld-linux.so.2 is unconfined_u:object_r:file_t:s0 instead of
system_u:object_r:lib_t:s0

This results in a failed boot of a refreshed image or newly installed image.

A workaround, for now, is to interrupt the boot and insert selinux=0 with the
boot parameters. (An unmodified followup boot, will trigger a filesystem
relabel, and things are then back in order.)

--Fred