The only ways I can think of where you can change this is using a java action or by downloading the database backup from your environment, change the required tables in database (e.g. using PGAdmin for Postgres) and create new backup and restore this backup to your environment.
Hope this helps!
You can do it straight in the database on all fields, including created and changed date at runtime using com.mendix.core.Core.dataStorage() write a java action for this, e.g.
'UPDATE "public"."'+tblnam+'" SET "createddate"=\'2000-01-01\' WHERE ID='+obj.getId().toLong()
Just never try taint guids lol