You can electroplate any hard plastic with a thin layer of metal. There is only one condition: the surface must be very smooth. This is not the case with unprocessed 3D products.

Electroless nickel plating on dielectrics is often easier to implement than electroplating. There is plenty of literature - see for example

Electroless nickel, alloy, composite and nano coatings - A critical review Sudagar, J., Lian, J., & Sha, W. (2013). Journal of Alloys and Compounds, 571, 183–204. DOI: 10.1016/j.jallcom.2013.03.107

There are also many commercial suppliers for electroless nickel plating services; some of these may agree to plate a test piece for you.