I tried to analyse this further and see that you need to spend much time to make this work. You need to update the input form(xtk:workflow) as well as data schema(nms:workflow -> you may extend the data schema and update the changes). You need to refer the new form that you're updating in the input form. Attaching screenshot. Hope this helps. But not sure how far this is reliable as that shouldn't impact anything else in workflow. Try to get support from Adobe support.
If i understand well, you want to duplicate a delivery activity and change the action to prepare and start.
If all of that is happening inside the same workflow, just select the original delivery activity and the Ctrl + C , then click an empty place inside the workflow and Ctrl + V . then in the copied delivery change the action to prepare and start.
I tried to edit the Workflow xtk, Copy pasted the same code which is for delivery. Rename the form but it was not visible as new one in action tab.
But when i tired to edit the exiting one and disable start and prepare it worked. But i need two activity one original delivery activity and another should be duplicate with disable start and prepare in it.