I'd like to know too... I tried to use Pastebin's API (weird I know but I just need to save texts and it works for my purposes) but it was needlessly complicated and didn't manage to get it working. Even though Pastebin says that you can do it without the API you can't really because of some CORS issue.
I read somewhere that if you use itch.io's Butler when updating in some way you could keep it but I don't know much about it. Most of the info I found was from 3 years ago, was hoping that was not still an issue :/