9.5 Can I safely de-install an old kernel package, and if so, how?

Yes. The kernel-image-NNN.prerm script checks to see whether the kernel you are currently running is the same as the kernel you are trying to de-install. Therefore you can remove unwanted kernel image packages using this command:

     dpkg --purge --force-remove-essential kernel-image-NNN

(replace NNN with your kernel version and revision number, of course)