Preserving Customizations
If you have made changes to imported objects in the target instance that you want to preserve, use the Move operation to move the customized object definitions into a different Domain.
The Move operation keeps references intact, so that instances of each moved definition continue to point to the same definition in its new location.
The import utility performs a check so that it never overwrites an object instance that points to a definition outside the imported Domain, even if the object instance is included in the import.
The utility does import definitions from the source that correspond to the definitions you have moved, but they have no effect because no object instances use them.
Parent topic: Exporting and Importing Objects