I'm trying to do a bulk tidy-up of Address fields in CiviCRM 4.7 by exporting the data, manipulating it in a spreadsheet and re-importing it. This involves moving some values around between postal address fields, requiring some to be blanked. The Import option for Duplicate Matching can only be 'Update'. However, if I include a null value for any field it does not overwrite (blank out) an existing value, resulting in duplication. Only non-null values are considered to be updates.
Example: trying to move "121b Baker Street" from 'Supplementary Address 1' to 'Street Address' using Import/Update results in both these fields containing "121b Baker Street".
My problem is a more general case of the question at Uploading null email address which refers only to blanking of email addresses.
Unless I'm missing something, I'd like to propose another option for Duplicate Matching (alongside the current Skip / Update / Fill / No duplicate checking) called 'Edit'. It would allow the removal of existing values by overwriting with a null string but would otherwise behave in the same way as Update.