SetHtml is basically a wrapper for a $("#id").html("<new html>"), so the
question is that yes if you invoke a JsCmd on Load / whenever you press a
button you can make the Html change the whole page. I wouldn't recommend
this and would instead look at a client-side library for full rerendering
of a page.

If you want to do it then do this:

def render = "*" #> OnLoad(SetHtml(myId, <div>NewContent</div>))

If you want to call it via a button just use SHtml.a or Shtml.button with a
SetHtml command on callback