Tags & Plugin

I didn’t know where to post this request so I thing the best place was here.
Does someone know about a plugin to really works the tags out.
Running an Historical Blog isn’t not easy with the tags generated … I have actually about 17.000 of them.
What I would like to do is to be able to merge some of them ex : Belgium with Area Belgium or ex : Brig General George S. Patton with Gen George S. Patton.
I would also really like to list all the unused tags and erase them.
And so on …
Thank you
Gunter