Wikipedia – How to Find Pageview Count of All Articles in a Category

If you go to the page for the Infobox Template, the "What links here" link in the toolbox will tell you all of the pages that use that template. In this case...

http://en.wikipedia.org/wiki/Special:WhatLinksHere/Template:Infobox_martial_artist

It's not directly possible to do that. But some wikis do have bots that can assist you with moving the items from the old category to the new one.

For Commons-specific information, including how to request renaming both to run, see Commons:Rename a category. I expect other large wikis will have similar pages.