The recommended way to modify the Wiki portlet configuration to recognize a new public render...

Create a hook plugin and add the public render parameter definition to portlet-custom.xml

Create an Ext plugin and add the public render parameter definition to portlet-ext.xml

Create a portlet plugin and re-implement the logic of the Wiki portlet and define the new public render parameter in portlet.xml

Create an Ext plugin and add the public render parameter definition to portlet-custom.xml