Yes, you have to alter the existing translation files, and that is a good thing.
If you change the English wording, the translations probably need to change, too. Even if they don’t, you need someone who speaks the other language to check.
You prep a new version, and part of the QA process is checking the translations. If the English wording changed and nobody checked the translation, it’ll stick out like a sore thumb and it’ll get fixed.