MikeB: It appears that the Sales Rep ID field (ie. the only one of the 4 sales rep fields I was "allowed" to explicitly import) is the basis/key field for populating the remaining 3 sales rep fields (SalesRep_RecordID, SalesRepName, SalesRepRecordID).
To update the SalesRep you only need to import into the SalesRep field, you won't be able to update SalesRep_RecordID and SalesRepRecordID.
MikeB: Near the bottom, the user was asking a similar queastion. Method wasn't showing "Entity Type" as a field in the drop-down that could be selected. So, "Do Not Import" and "Create New Field" are the only options. If it's a derived field, then creating a new one would create some problems, no?
You won't be able to create a new FullName or EntityType field - you won't be able to create a duplicate of any field.
~C