Editing tags???

Hello everyone! Thought I'd come back cause you were all very helpful last time!

Hypothetically, if I implimented a tagging system but then wanted to change it is there any way to edit the existing tags rather than deleting them (eg; the mass post editor/tag replacer on tumblr) ?

I haven't been able to find anything and I just wanted to ask because I feel like this would be super super useful, especially as communities get bigger.

Thanks! - Miri