The Revit model was updated and I exported a new SPX file. How do I bring those changes in without losing the resource assignments?

1. Open the External Data window from the Navigator ribbon
2. Find the originally imported SPX in the list
3. Right click on the SPX name and select Synchronise From

4. Browse for the updated SPX
5. Leave the Synchronisation settings as default:

Existing/updated objects will remain assigned to tasks. Only new objects will need to be assigned.