Aside from manual or core service scripts consider the PowerTools PowerShell option, compliments of Dominic Cronin, or Content Porter, especially useful to set defaults field values.
PowerTools 2011 has (a PowerShell Version of) Component Synchronizer. Dominic Cronin created a PowerShell version of Component Synchronizer branched within the PowerTools repository. If interested in helping, definitely reach out to see how we can integrate this into the CME Extension.
Content Porter . I've yet to try it, but Content Porter 2009 SP2 has an option to Synchronize content against Schema before importing.
SDL Live Content explains importing items without their schemas may mean they "may not be valid against the Schema found on the destination Content Manager."
But if you select Synchronize content against Schema before importing, Content Porter will attempt to:
- Reorder fields to match the [target] Schema
- Remove fields not present in the [target] Schema
- Add fields to items, "on the condition that the fields are optional fields, or have a default value, or both."
This handles the typical schema changes, which I've outlined in this post.
Update: I describe Content Porter component syncrhonization on TridionDeveloper.
Warning: any synchronization approach can lead to data loss. Be sure to back-up and test your approach in DEV before automatically changing components. It's called PowerTools for a reason. ;-)