Changing to 'sensitive' retrospectively

You can edit records by going to 'my records' , finding the record you want to make sensitive and then using the edit icon (looks like a pencil on paper). You can then tick the box to obscure the record and set what level you want to hide it at. I think that if you do the same to a record added using  the 'add list of records', then probably doing that once will obscure all of the records added at that time, although I've not tried it. Obviously this will take time if you have lots of records you want to go back and make sensitive. Keep in mind that if some of these records have been verified and/or been on iRecord for quite a while then they might already be on the NBN Atlas by now.