Hi bmarbury
In 2.x you could disable the behaviour of the Auditable aspect, but as of 3.1 AuditableProperties (like cm:created) are managed directly at the node DAO level. According to comments there, auditable properties are never set manually (and the code explicitly forbids it).
It's ok as long as you see these properties as records of what happens in a given instance of Alfresco (even an upgraded one). However if you need properties that mean date of creation externally to alfresco and that are manually set, consider defining your own properties for this purpose (like author vs creator properties).
Regards,
Marc