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Initially, the configuration checked as "Is default configuration" will be the active configuration. In order to change it to another configuration, select "Options" then click on the configuration that is displayed next to "Using Instance/Occurrence Configuration", then you can select another active configuration (refer highlighted below):
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If the User synchronizing data between Family Instances and Item Occurrences does not have Rights to change Occurrence data within dRofus, only the Family Instance Parameters within Revit will be updated but not the Item Occurrence Attributes contained within dRofus.
As dRofus Item Type attributes and Revit Family Type parameters are also available within the Instance / Occurrence Configurations, it is possible to also use the Instance / Occurrence Configuration to push values from dRofus Item Type Attributes (such as "Item Name", "Item Number", "BIM ID" etc.) into Revit Family Instance Parameters. Similarly you can push values from Revit Family Type parameters (such as "Type Name", "Type Mark" etc.) into dRofus Item Occurrence Attributes.
Values for From and / or To parameters for Doors and Window Family Instances in Revit can also be pushed in to Item occurrence attributes in dRofus when using the Instance / Occurrence configuration.
More about syncing Family Instance data with Item Occurrence data on a one-by-one basis within the dRofus Panel can be found here: dRofus Panel Family Instances Action Icons.