I think the reasoning behind the word choice in the ceremony is that the Keyblade is considered a singular entity by most characters in the post-Chi era. It has many wielders with their own unique blades, but they all seem to stem from one unseen force that chooses who is worthy to actually wield it, regardless of the whether the ceremony has been performed or not. That’s why it is typically said that one wields “the†Keyblade rather than “a†Keyblade, despite some exceptions.
Way to Dawn was born from Soul Eater. If Terra passed on his Keyblade, that would have been the Kingdom Key. So what would that have to do with Way to Dawn since it’s an entirely separate Keyblade? It’s more likely that Way to Dawn breaks when Aqua attacks him because Riku has completed the journey he needed it for.