[Plone-UI] Problem with customizing comments.pt in plone 3.3.5

[redCOR AG Gerhard Hug]

Hi

To get a special adaption for a client I have to change the look of the
discussion/comment area in a document (plone 3.3.5)
The name of the template placed in browser/templates is "fhnwcomments.pt".

What I did in configure.zcml:    
<!-- Render comments -->
    <browser:viewlet
        for="*"
        name="plone.comments"
        manager="plone.app.layout.viewlets.interfaces.IBelowContent"
        view=".interfaces.IThemeSpecific"
        class=".viewlets.CommentsViewlet"
        permission="zope2.View"
        />
an in viewlets.py:
   from Products.Five.browser.pagetemplatefile import ViewPageTemplateFile
   from plone.app.layout.viewlets.common import ViewletBase
   from plone.app.layout.viewlets.comments import CommentsViewlet

   class CommentsViewlet(CommentsViewlet):
       index = ViewPageTemplateFile('templates/fhnwcomments.pt')

Restarting works without problem but the changes in the made in the new
template aren't shown.

Can anybody tell me what i did wrong?

Thanks a lot for answers
Gerhard