When does Import consider page templates to be the same and re-write them?

If you import some page templates or stylesheets into an existing installation, the import process can re-write some existing objects. It happens when:

1. the objects have the same GUID-s and
2. they have the same code names.

That is why it is not enough to change their code names if you want to keep the existing objects and import the new ones. The future versions will support a general Clone function for all objects.