you can rename the slug too. topic links will work because they don’t use it in their url:
https://meta.discourse.org/t/does-renaming-my-old-categories-requires-any-other-changes/402804
https://meta.discourse.org/t/-/402804
https://meta.discourse.org/t/402804
have you tried using a test category with existing topics and then renaming it and its slug?
eg:
rename existing category and it’s slug
topics are still there:
