- Set your Rich Text field to  "Store contents as HTML and MIME".
 - Bind your Rich Text control to a scoped variable (requestScope.Body).
 - AddSSJS to afterPageLoad event.
 - var entity:NotesMIMEEntity = document1.getDocument().getMIMEEntity("Body");
 - if (entity != null) {
 -     requestScope.Body = entity.getContentAsText();
 - }
 
Then in your querySaveDocument you can call a function similar to the one below:
 
function updateBody( doc:NotesDocument ){    
    if (requestScope.Body != null) {
        //requestScope.body is bound to an inputRichText control
        var body:com.ibm.xsp.http.MimeMultipart = requestScope.Body;
        var stream:NotesStream = session.createStream();
        stream.writeText(body.getHTML());
        
        var entity:NotesMIMEEntity = doc.getMIMEEntity("Body");
        entity.setContentFromText(stream,"text/html;charset=US-ASCII", 1725);
        stream.close();
    } else {
        requestScope.status = "no content";
    }
}