Board Thread:Support Requests - Getting Technical/@comment-1158325-20140907034032/@comment-168424-20140913154127

The above CSS basically just prevents using of CategorySelect, but if that is good enough, you could try it.

Technically it is violating the ToU if you use it site-wide because it alters the Wikia UI. Maybe you could also ask Wikia to turn off CategorySelect on your wiki, but they may not allow that either.