Oh - nearly forgot! It's fairly simple to retro-fit a zero fret - the fret simply goes on the end of the fingerboard where the nut would be, with a small piece of suitable wood glued in place to secure it. The nut is then replaced.

If the truss rod adjuster screw is at the nut end of the neck, a little kerfertling (technical jargon! Hah!) may be necessary to get everything accessible, but it's no big deal!