The following is a feature request from Patrick Conrad:
Adding an ability to create new subscribers/publishers
For example, if the user created a script that propagates for one day and they want to add a new calculation to the list of sc parameter calculations that are reportable at each propagation step, they can not. Currently the user would have to split the one day propagation into several chunks, most likely using a control flow command, and output the desired calculation at each one of these smaller chunks.
See Steve Hughes for more insight into how this can be implemented