In Navigator>External Data, select the name of the model file
Right click and choose Synchronise From
Browse and select the updated model file
Modify import settings if desired
Results will be reported
For objects that maintained the original GUID, the resources will remain assigned to the tasks
To find new objects that need to be assigned to tasks, drag the focus time to the start of the project
In Synchro, go to Help>Search and search for "Synchronising FROM a 3D Graphics File" to see step by step directions with images and descriptions of the available settings.