Face = identity, so removing your face = forfeiting your identity. But with the doppelgänger reference, maybe it would be more accurate to say that R removing his face = forfeiting his identity to Y. But the fact that he keeps the face to use as a mask could then be interpreted as him still superficially clinging to that old identity. But now instead of "being mistaken for Y," he's "disguising himself as Y." So when he reveals himself, he's doing just that. He's no longer correcting people, he's revealing his "trick."
In terms of the manga's themes as I've theorized about in previous comments... I guess the "alternative definition of seeing" might have something to do with identity and recognition, then? Chapter 17 also had a focus on faces, and the centipede there having the eyes of the people in the photographs could be connected to the idea of "taking an identity" which is embodied by their faces. So like how in this chapter, R gives up his face so as to forfeit his old identity to Y, the centipede takes other peoples faces to build up its own composite identity.
Also, I'm a bit curious about the "censorship" of the names in this chapter, using just the single letters "Y" and "R." Names are also associated with identities, though not to the same extent as faces, of course. So the abstraction of their names might be related to the abstraction of their identities as a whole, maybe? Which could then be related to the fact that they're both confused for each other. The fact that they're both "abstracted" might be what caused them to be confused for each other.