Are you just looking to modify the create dates and other dates of that nature?

If they are in the database you should be able to update them, I would make a database backup first prior to playing with it though.

The Repository module can't prevent you from making db changes directly, so I'm not sure what you mean by "Repository module doesn't allow".

The Repository items are stored in the grmRepositoryObjects table. Each item has a CreatedDate and an UpdatedDate column which stores the date the item was initially uploaded and the last date the item was edited, respectively. You can certainly edit those values directly in the db or via sql script if you need to.