So decided the placard wasn't enough and turned the idea into a lightbox. I apologize I ran out of black filament so I haven't printed this myself yet, but everything looks like it should work.

Diffuser Plate has a couple small pegs that align it with the Front, and small pegs on the back will also align it to the front. This can be printed with or without the diffuser plate, and alternatively you can print the diffuser plate and remove the assembly part “Star Wars Card Light Box Seal Diffuser.stl” and print a lithophane to fill that spot. There is a negative shape in the file to make it the same as the opening in the design.

I imagine this should be able to clip on to the front under the little tabs, but depending on printer variances you may have to adjust the scale by 1-2mm.