Welcome! An upgrade is not required if a category set changes (at least in the past).
When category sets change, it is a manual update, which simply involves clicking a button. I dont have a MWG which requires a category set update, below is a crude rendering of what you can expect:
I'm guessing you may have read Re: Problem blocking Consumer Protection category
For reference though, in my 8 years categories have changed about 3 times (very infrequent).
Something of that simplicity is what i would have expected.