Hi,
What I recommend for this type of uses cases is a change of approach:
1) Use a "Raw Data" table for the import task
2) Use a "_TR" table for the treatments (formulas, hide)
3) Use a " MAP" table to aggregate data
Therefore, if the source file changes, then you import it to a new "Raw Data Table", recreate another " TR" for treatments and aggregate it to your "MAP".
With this method you don't loose the continuity.
Thanks.