I don't think it's possible to "put limits" like this. Whenever you interact with someone, you inevitably change each other. You can – to different degrees of success – resist the change, but this requires applying a force in the opposite direction, and you risk reinforcing your own beliefs too much.
It's also entirely possible that someone you've never met creates a change on you by changing the social imaginary (the shared realm of ideas and symbols) first.
As for my impression of the meaning of this chapter: I believe that, by wholly destroying the barrier between the physical and the imaginary, Big Sis' invention is meant to expose just how vulnerable we are to changing each other. By literally merging with the world, people here have surrendered to the currents of social forces.
The only people capable of resisting this are people who have reach the level of self-realization within the Maslow hierarchy of needs (Yuuri and Chito in the train), as they feel whole and secure within each other's presence, or highly individualistic people (Shijima who's a loner).
