Import from CSV to all Products

I imported our data into the AHA trial.  Then I organized my initiatives into a product hierarchy.  Then I realized that my start and end dates were in the wrong format.  Start date of 4/1/2019 went into AHA as start date of 1/4/2019.  My fault.  However, I find I cannot reimport that field, without either, importing each product individually or destroying my product hierarchy.  It would be nice to have the capability to import a field for all existing initiatives without disturbing the product hierarchy.