Right after you figure out how to 3D print solid rocket fuel without things going 'bang' prematurely.

If you print Potassium Nitrate/Sorbitol[0] with direct granule extruder[1] you could do it. But this will probably need additional toolhead for engine body[2] (plastic-fiber composites DO have enough strength to survive using KNSB in engine, I've seen tests, but those are not publicly available) and for ceramic nozzle[3]. With some experimenting, probably doable.

[0] http://www.nakka-rocketry.net/sorb.html

[1] https://hackaday.io/project/181165-my-machinery-2021-direct-...

[2] https://www.sciencedirect.com/science/article/pii/S221282711...

[3] https://reprap.org/wiki/Ceramic_Extrusion