Hey @Sam_uk,
If you are self-hosting you can indeed change this string.
You can find the string in baserow/web-frontend/modules/database/locales/en.json, in there you have to go to rowEditFieldMultipleSelect.addOption, you can also just do a string search for “Add another option” in that file to find the correct field.
Keep in mind, there are several .json files in that directory, that will translate the string into different languages. If you just care about english, it’s fine to just change it for english, but be aware that it remain the same in the other languages (unless you change them too).
Let me know if you can’t find the entry or if you have any other questions 