Set Public Render Parameters in Theme

You can use the following tag to reset render parameters from theme -
<portal-navigation:navigationUrl type="launch" keepNavigationalState="false"/>
It is described under the following link - http://publib.boulder.ibm.com/infocenter/wpdoc/v6r1/index.jsp?topic=/com.ibm.wp.ent.doc_v6101/dev/dgn_ptlnavig.html

<portal-navigation:urlGeneration/> tag can be used together with <portal-navigation:urlParam/> to pass action/render parameters to a portlet.

It is described under the following URL - http://publib.boulder.ibm.com/infocenter/wpdoc/v6r1/index.jsp?topic=/com.ibm.wp.ent.doc_v6101/dev/dgn_link.html