Replacing a single typewriter key legend:

The keys on these are metal bases with a cardboard legend (with the glyph printed on it) which is typically covered by a clear acetate lens and held on by a metal keyring. Fortunately you've got the keyring. If you can't source a single acetate lens from a repair shop you can buy a set from https://mytypewriter.com/products/hello-qwerty-replacement-keytop-disc-set

Richard Polt has some of the process described here as well as as high resolution scans that you can use to print out the key legends you may need. https://writingball.blogspot.com/2016/10/legendary.html

Ames Supply Company used to sell keycards for doing this. Some of them had colors including green, so keep this in mind if you try something like creating rainbows across your keyboard or other visual fun. https://typewriterdatabase.com/1960-Ames_Gen_Cat_10-March.misc-supplies.manual

Our friend Lucas Dul of Chicago Typewriter has a great YouTube video of the tool and some of the process, though you can probably get away without a pair of custom pliers since you only need to do one: https://www.youtube.com/watch?v=jYHrBjfQxpM

As a fun example, Heiko Stolten recently did a whole keyboard on a Remington using custom made legends that use the font from the Netflix series Wednesday: https://www.facebook.com/groups/TypewriterCollectors/posts/10163537426144678/ If you ask nicely, they've got the original files if you need them for printing out.

Good luck!

reply to u/saved_rae at https://old.reddit.com/r/typewriters/comments/1uvehmb/missing_period_key_repaint/ who was missing a period legend and the acetate lens.