Well... it is an example workflow and the script is documented.
It would run in either case... but you will want to understand and tailor the script to do what you want.
Basically, there is a workflow in the VCAC portion of the Library workflows that allows you to perform a resource operation request on a catalogresource. You can literally just run it and supply the values... if you see the Operation for Change Lease, then your service account for the plugin to vRA is configured properly in your BusinessGroup to see the ChangeLease Action. (it can be the only one that sees it if you want)
Then you can BOTH create a new CUSTOM Resource Action (provided you have ASD... which you do in your case), for change Lease (with date constraints that are missing in the current out of the box action), AND use it as part of your provisioning workflow if you so desire.
In either case you would want to supply the proper inputs to the provided Library workflow which includes the CatalogResource (virtual machine), the Operation(Change Lease), and the property values for the Operation. (in this case, a valid datetime)
With the ResourceAction method, the user makes a request for your custom change lease, and then the service account makes a request for the actual change lease passing through the values you allowed in the initial workflow if valid. So you will see two requests in history. One as the user. One as the service account.