In the late 1990s and early 2000s, several companies (Okidata and ALPS Electric, and I think others) offered ribbon cartridge printers which had the ability to print special inks such as white and metallic colors. These printers and their supplies were very expensive, but they were a boon to the scale modeling community, and many modelers bought these printers in order to produce custom waterslide decals for scale models.
As a model railroader, I knew a friend who owned an Okidata printer and I often commissioned him to print decals for me, including a run of re-dating decals for NGM slipcases. He used Microsoft Word to create the artwork - the included font Cheltenham Condensed Bold 20 point is an almost exact match for the typeface used on modern commercially produced NGM slipcases. I acquired a number of secondhand slipcases and used a mix of various art store acrylic paints to create a match for the slipcase maroon so I could paint out the old numbering (and in some cases the month lettering too) and apply new decals in place of the printed lettering/numbers.
Thankfully I had him do enough for my needs all at once, since his printer (almost 20 years old at that point) ceased working several years ago. These kinds of printers are long out of production and I'm sure the number of folks out there with working printers and the supplies to run them are hard to find. I don't know anyone else in my circle of model railroaders who still has one, but maybe someone who's more adept at social media than I am can reach out and find someone. It was really nice while that technology lasted, but for some reason it seems it never really caught on...