thread_reaction apparently has a user name field, but no rename support.
I don't know if this feature is actually active anywhere.
See https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FLiquidThreads.git/7dab2acbd0d554053ce79e18fa21387e424a705d/lqt.sql#L98 and https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FLiquidThreads.git/7dab2acbd0d554053ce79e18fa21387e424a705d/classes%2FHooks.php#L282