Just a short note for myself...
To move a dpkg-managed file out of the way:
dpkg-divert --rename --divert /usr/share/initramfs-tools/dropbear.original /usr/share/initramfs-tools/scripts/init-premount/dropbear
Copy and edit original.
cp /usr/share/initramfs-tools/dropbear.original /usr/share/initramfs-tools/scripts/init-premount/dropbear
ed /usr/share/initramfs-tools/scripts/init-premount/dropbear
