That's assuming Disney could ever register the trademark, which is not a given, no matter how often they use it.
That's assuming Disney could ever register the trademark, which is not a given, no matter how often they use it.
Disney can and will allege that the disclaimer fails to prevent confusion and take you to court regardless. And then you have a legal battle to prove that it does “fix that.” A legal battle that will cost you millions of dollars and years of your life, neither of which you will get back even if you win.
For trademarks, there simply is no safe harbor, and thus no conditions under which it can be removed. That means there isn't a codified process for YouTube to follow; but the stick they can be beaten with at the end of the day -- infringement litigation -- is the same in either case. You can bet they'll do what they can do avoid it.
If you're making a work derivative of Steamboat Willy then Disney has no basis to sue you, regardless of what trademarks they claim.