I used this calculated field in a query:
CalcDate:
iif([ImportedDate]="",Null,
DateSerial(Mid([ImportedDate],7,4),
(Mid([ImportedDate],1,2),
(Mid([ImportedDate],4,2)))
...and it worked. I still don't know how to programmatically change a field's data type using VBA, but I can base the rest of what I want to do in the Access database off the query with the calculated field CalcDate that changes the date text into true date data... so this works.
Thanks!!