If you've got it into official Xposed Repository or we can talk about here (and in modules section) I think they are legal. Because using it, you don't modified YT app permanently - just you've got another apps (modules) for overlay YT. Can use or only download/install it for testing this part of service if it's not available in your country. Exactly - if you can't use this part of YT (background) normalny, what can you do? In sum, no one can force you to throw them away, nor account for use since modules are available here. That's all I think about. Cheers.