According to this answer it isn't possible for normal users to unfreeze chat rooms.
It would be nice to be able to unfreeze rooms that were auto-frozen due to temporary inactivity without having to bother a moderator.
I am aware that it is possible to create a new room, but this is not so useful when there are existing links to the room. Also, if someone finds the first part of the conversation (whether via a link or via a web search), there is no obvious way for them to find the room with the continuation of the discussion (or even to know that one exists).