Board Thread:Support Requests - Designing Your Wikia/@comment-24831695-20150323064454/@comment-452-20150323153632

You're probably not allowed to do the first. The last time I asked, I was given permission by Wikia Staff, but then another Wikia Staff member removed it and accused me of violating the customization policy. However, other wikis still do, and Wikia Staff will not accept "reports" of Wikis doing it, so I assume they selectively enforce the policy on users/wikis whom they do not like.

That said, there is no "built in" way to change that menu, you need to use javascript to do it.

Google can help with the second