Can't customize text on custom button in template override using UI

Ah, I forgot to add that I did the template override in a new theme component that I created in the Admin menu, not in a separate git repo.

I tried doing it as such, by adding the theme-prefix in the label:

…but it didn’t seem to work.

Is it possible to add locales/custom text in a theme/component created in the admin page without having to create a git repo?