Once an update like this is made, how does the bootimage get updated?
(Delete MD device and recreate it? This ties back to my other question of getting Admin page created MD's to generate the bootimage files.)
The easy way out is to delete the image and recreate it. Since you didn't install anything in that image yet, I recommend you take this approach.
The other way would be chrooting into the disk image and uninstalling the kernel package. This would trigger a kernel reinstall next time images are checked.
Images are created and kernels installed at boot time by the Diskless_Setup.sh and Create_DisklessMD_FS.sh scripts found in /usr/pluto/bin. The first calls the second for each MD.
Just in case you wonder why I don't automate this: when you install the kernel, it creates an initrd on its own. Now, I could just create that each time, but it wouldn't be efficient for most of the users. The initrd includes some predefined modules, but not all, so I have to add modules to a config file used by mkinitrd in the kernel-image postinstall script.
I could check the initrd file when doing a kernel install though, so if we change the kernel version the initrd config file gets updated before the new kernel install.