Say I rename a tag called mc548 to mc548-unicamp, does that redirect the URL http://umamao.com.br/questions/tagged/mc548 to http://umamao.com.br/questions/tagged/mc548-unicamp?
EDIT:
Turned it into a feature request.
Since tags have more semantic weight on SE sites, it is common for people to bookmark them (at least in my case). Having the site redirect old tags to new tags when they're renamed would be a great help in that case.