Import custom field to fill duplicate contacts
One way to do it is to place these 200 records in a separate csv and add a column with the CiviCRM contact id and use that as the matching identifier. In that case you would also need to copy the records for each contact with the same email address.

Another one is to do the same, but then use the "external identifier" field as the matching identifier.

Quite a bit of manual work. 

All other solutions I see would be with custom coding (or custom import scripts).