Board Thread:Support Requests - Getting Technical/@comment-28083312-20170422024713/@comment-1757994-20170422030810

You can't stop the user JS from loading, but if you have some code in it that you want to run after he rail loads, you could write an async routine in your user JS to wait for it.

That would be easiest to do if Wikia has defined a MediaWiki hook for the rail loading, then you could hang the routine on their hook. I have no idea if such a hook exists in Wikia's code.