If this happens under EU jurisdiction, then you can deny the update and legally demand that the TV continues working. The manufacturer may not impose new rules after the selling contract.
Fuck this wild-west anarchistic behaviour of software companies. When we have legal protection, we can make use of it.
Also have a Sony Smart TV, and I live in the EU. After updating the TV, it asked me whether I wanted to enable Samba, and I simply declined. Seems to be disabled now.
The only way to be sure with untrustworthy devices like this is not to connect them to the network at all (i.e. use a separate device you can trust instead), or better yet, buy a dumb monitor instead.
Fuck this wild-west anarchistic behaviour of software companies. When we have legal protection, we can make use of it.