Dear @mmendes,
Unfortunately, this doesn't work as there is no Plain text control anymore in Public Web Forms, the Text control is actually Rich text, so the following code should work:
fd.control('Text1').$el.innerHTML = "Here I changed the text";
Dear @mmendes,
Currently, no update to documentation, though we're working on it. We're going to add a new property for the Text control to change the text directly, without using the $el.innerHTML property, but this method will keep working.