The default behavior can be changed to 'Unassigned' by modifying the system registry. Specifically, the property DataTransforms/PPV/defaults/domain/INITANALYSISTYPES should be set to 'N'. Changing this setting will typically involve having the system administrator perform the task -- most likely by requesting it through a change request form if the system is hosted at SAS.
We're working through this documentation right now, specifically as it relates to registry settings associated with the Process Editor. These may also carry over to the other applications. There are various business rules that can be defined in the registry (for example, all macro variables that begin with inds_ will default to input data sets, etc.). Documenting this detailed information is taking a bit longer than I had anticipated.