I'd simple would like to do something like this in a OS::Heat::SoftwareDeployment resource:

script_name: {get_param: deploy_action}

But it seems like deploy_action is a "derived declared input" and hence cannot be retrieved in the same way as a "classical" input in a HOT template. On the other hand, it is passed to ANY OS::Heat::SoftwareConfig script as input. Strange.

I had a quick look at https://github.com/openstack/heat/blob/master/heat/engine/resources/openstack/heat/software_deployment.py (the code), and while I really don't understand everything, I wonder if it is even possible.