This hook allows you to alter the location information that will be moved from the duplicate contact to the master contact.
This hook was first available in CiviCRM 4.7.10.
hook_civicrm_alterLocationMergeData(&$blocksDAO, $mainId, $otherId, $migrationInfo)
$blocksDAO: Array of location DAO objects. Formatted as follows:
[ 'email' => [ 'delete' => ['id' => object], 'update' => ['id' => object], ], 'address' => [ 'delete' => ['id' => object], 'update' => ['id' => object], ], ]
$mainId: Contact ID of the contact that survives the merge.
$otherId: Contact ID of the contact that will be absorbed and deleted.
$migrationInfo: Calculated migration info.