1) I would HOPE that actors do not change their performances based on reviews! Generally speaking, once a show opens it is what we call "frozen" and performances change very little.
2) Several people in the theatre community, including actors, do read these and other message boards. In the past, some have posted, yes, including Marc Shaiman, Lin-Manuel Mirada, and Anthony Rapp.
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle