Say I have created a shared module with 2 portlets in the same. I have set the preferences for certain fields to value A, B, C for e.g.. Now user has downloaded the pre-configured pages into their private dashboard.
User has updated some other preference field values as needed by them.
Now assume, I want to change the preferences I had set it as A, B, C to A, B, D in the module and I want the same to reflect to all the user private dashboard where they have added this module already.
I don't think its possible to achieve that since private dashboards are a copy of your public dashboard. Also I haven't check where the preferences are saved on the PPM tables but could be an option to do a mass update if you manage to identify the portlet and preferences to update.