What I would like is to change the value of the class attribute of the <a> tag depending on a parameter passed from the node_view_gui call. I'm aware I could have 2 line templates and simply change the 'view' parameter between the two, but would prefer the first solution.
I suggest, that you use "classification" for this.
See http://ez.no/developer/ez_publish_3/documentation/customization/components/datatypes/ezxmltext/classification
and
http://ez.no/developer/ez_publish_3/documentation/customization/custom_design/override_templates Based on classification, you can create override template, but I think, that the "classification" text is also available to the template, so you could use one template and decide in this template, what do do.