I propose a new method of producing smaller amounts.
The image(s) to be generated are created as a hexagonally-packed bitmap, which approximates a circle.*
The sugary glop is prepared in various colours as normal, then fed into several hoppers of the rock printer.
The first stage of processing is to split the coloured glop into pellets, which may be spheroid, disk or short tubes, depending on which works out the easiest.
The second stage is to assemble them into the hexagonally packed array, probably using a mechanical arm.
Finally, the array is rolled, to produce one tube of rock.

This might work quite well in a production line; you could sell individualised rock with ordering over the internet or mailorder.

Inspired by the 'readable rock' idea (linked)

*This is hard to describe. the arrangement of the pixels is as hexagons, because they pack more closely. The shape of the bitmap approximates a circle, by having the corners blank.
(On second thought, if square cross-section pellets can be made, this would make generating bitmaps easier, as there is already a wealth of software to do so.)