Congratz on beating the game.

Unfortunately, this isn't possible as far as I know. I asked over discord and someone confirmed that it isn't possible.

The best thing you can do is open a notepad/document and copy paste your librarian info.
Copy their name, the numbers that represent their hair and eye type, their size, and the colors for their hair and eyes.
Then copy all the dialogue/phrases.

When you unlock a librarian, refer to your notepad/document to edit them to match and done!

It'll take a bit of effort, but it should work.
I've seen people do this over twitch chat to get their personalized librarians into the streamer's game.

Btw I have beated the game about 250 hours ago, but thanks.
Also thank you for your research in terms of nugget saving.

♥♥♥, 40 unique librarians... I think it is too tedious work for me. It's good that I saved the files of my past run and my chibbies did not disappear.