I believe you need to create a custom shelf script that instantiate the 2 nodes. This is separate from creating the HDA itself.
Here is the content of the shelf tool labeled
Karma from this file:
$HFS/houdini/toolbar/ExtraLopTools.shelfimport loptoolutils
node = loptoolutils.genericTool(kwargs, 'karmarenderproperties', 'karmarendersettings')
node.setCurrent(True)
nodename = node.name()
kwargs['inputnodename'] = nodename
kwargs['inputs'] = [(nodename, 0)]
kwargs['nodepositionx'] = str(node.position().x())
kwargs['nodepositiony'] = str(node.position().y() - 0.5)
rop = loptoolutils.genericTool(kwargs, 'usdrender_rop')
rop.parm("rendersettings").setExpression('chs("../%s/primpath")' % nodename)
rop.parm("husk_instantshutter").setExpression('1 - ch("../%s/enablemblur")' % nodename)
node.setCurrent(True)
node.setSelected(True)