Modifiable System Field

Hi,

In one of Dataloader tutorial I got following point -

If "Modifiable System Field" configuration is enabled, then system fields (like creation date) can be set to any value during initial data load. These values can however not be updated after the initial upload. These fields are accessible through the API. These are backward compatible with all SOAP based APIs available for all custom objects. These are Read only fields.

So, Is it possible to set initial value for system fields? If yes then Can anyone tell How to enable "Modifiable System Field" configuration for system fields? or where I will found setting for system fields?

Thanks.