It's on the internet, it exists to be modified. Tis the law.

With that said, if I heard that, I'd either do things low profile or I'd not do it at all, because at any point the devs can just intentionally ruin whatever you use to make your app work. And low profile isn't an option, RiF's dev will always have at least a couple hundred who will try whatever they make, day 1. In their shoes, I would contact the Tildes dev directly and ask where we stand, then go forward with blessing, or leave.