The mouth speaks what is in the heart. What is inside eventually leaks out. In anonymized spaces, this is especially true, and has been acknowledged from the beginnings of the internet (and perhaps long before). When you don a mask, your heart speaks freely.
But the knife cuts both ways. As you speak, so will your heart be. I think modern psychology supports this. Actions drive attitude, and attitude drives actions. If you assert your will in either place, the other is disrupted and will adjust.
You can literally change yourself into whoever you want to be. But a passive participant in this process will simply show the world what kind of person they are without ever realizing it.