The biggest problem with renaming a branch, is that you will effectively be performing a baseless merge next time you merge to or from the renamed branch. This can cause a lot of pain.
I’m currently trying to untangle such a mess at the moment and its not pleasant. (Branch was renamed 4 months ago. The first merge from the branch was partial) its a nightmare I wouldn’t wish on my worst enemy (who coincidently are the devs who renamed the branch and did the partial merge)
See this answer for more info