Calling setContents() after setContentsURL() in HTMLFlow

Sometimes I want to use setContents() on HTMLFlow, however when setContentsURL() was used/called first; setContents() has no effect.

Is it possible to call setContents() after the HTMLFlow is rendered and setContentsURL() already called?

Also, what is the correct way of setting contents, if I want to include my own stylesheet for the html that I'm setting?

Thanks